Hi again and sorry for the tardy reply; I check in on the forum almost daily but don't always see every topic!

Before answering any of the above questions, I'd like to say, as someone whose interest in Buddhism began at age 15 (I am now close to 21), let me give you a piece of advice that I have given many times on this board: approach your research and your decision-making with a Dharmic attitude, with patience and mindfulness.  I could not emphasize this enough: practicing Buddhism does not preclude formally converting.   With that
caveat, I'll respond briefly to your questions and if you're interested, I'll provide links to more in-depth info.

I want to be a Tibetin Buddhist.
I am wondering what are their basic beliefs?

Tibetan Buddhism is essentially the form of Mahayana Buddhism that flourished in India in the first millenium CE,
and began to imported into Tibet in the 8th century.  There are cultural accoutrement which are characteristically Tibetan, but the outward appearance has very little to do with the actual teachings.

The beliefs of Tibetan Buddhists are fundamentally the same as those of other Buddhists.  All other forms of Buddhism could be categorized as Theravada or other schools of Mahayana.  All of these share the
same foundation of the scriptural tradition of the Pali Canon.  The Tibetan tradition shares with the other forms of Mahayana the scriptural teachings of the Mahayana sutras, which Mahayanists call the Second Turning of the Wheel of Dharma.  The most important difference between the Tibetan tradition and all the rest is that it contains the teachings of Vajrayana, the Diamond Vehicle, also called Tantrayana.  This is the vehicle of tantra.  In tantra, in contrast to the sutra teachings, one "generates" oneself in the aspect of a tutlelary deity, or yidam, which means meditating on one's identification with the wisdom mind of the deity.  It is a relatively fast path to enlightenment but is not for all practitioners. 

In sum, all the teachings of Buddhism were taught in three big cycles, or turnings of the Dharma Wheel.  Tibetan Buddhism is the continuation of a tradition which combines all three, the two sutric and tantric traditions. 

Is there a specific initiation ceremony to undergo in order to become one?

No.  In all traditions, one can take Refuge, which means taking the Buddha, Dharma, and Sangha as one's guides to enlightenment.  This is an actual practice which one does one one's own, but making a formal commitment by taking refuge with a Sangha member(ordained monk or nun) can be very beneficial if you are so inclined.  However, as long as you can generate refuge in your mind, it is not absolutely necessary.

Can I become a Buddhist Monk?

Yes.  Go to college, then live the life of a monastic for a few years before you actually take vows, though.

How?

First you would have to take Novice vows from a fully ordained monk.

What do Monks do?

It is a difficult life, certainly not for everybody.  You cannot own anything besides one or two sets of robes and a bag, you cannot sleep on a real bed, you cannot have more than two meals a day, and never meat.  The restrictive disciplines that ordained Sangha must practice are many.  In short, it is miraculous that the conditions for fully ordained sangha to exist are available at all these days.  The rules governing the behavior of monks and nuns is defined by the vinaya, the monastic code.  The breaking of some rules constitutes a minor violation which can be mended with confession.  Committing other violations means that one is no longer a bikkhu,, or monk.

Monks do not perform a priestly function in Buddhism.  The Sangha as it existed in Buddha's day was a community of virtuosi who took vows of their own accord for the purpose of their own enlightenment.  They would be supported by the lay community by means of small offerings, and in return they would share their experiences in the form of teachings.  This is still the ideal, though in many Buddhist cultures, monks play a role comparable to that of priests in other cultures.

In the Tibetan tradition, monastics can take a variety of paths, from pursuing a traditional monastic education (a geshe is a master of the scholarly tradition) to becoming a hermetic meditator. 

What is some good online reading?

www.lamayeshe.org
www.thubtenchodron.org
www.fpmt.org
www.lamrim.com

How do you decide Buddhism is right for you?

The answer to that one lies with you.  You are young, and you have plenty of time to research and find your path. 
Don't be hasty. 

LozangK
Beliefnet Host, Buddhist Teens

Hello there, I do have an answer for you:
To begin with, I grew up in a multi religious home, father was a catholic, mother was prostant.  In my years of travel through this life time, I had to take the time to think about what I wanted to believe in.  There is no correct answer for what you are asking, from anyone but you.  It was stated by His Holiness the Dali Lamma, that when you decide to change your belief system, you should take the time to think about what you are wanting to gain from such and then do a bit of research on it.  Do not make a hasty decision as what may work for some, may not work for others.  There are many sects of buddhism, and the prior replies to your questions are quiet good.  I would say if anything, if you can not check a book out of the library, then what is to stop you from sitting down and reading one or 2, or even doing some reading on the internet.  A lot of information is out there, but you need to read ask yourself if you are wanting this for yourself.  I do disagree with the prior post on meat as HH did state that it all depends on where you live and the dietary needs of the body at hand, so some buddhist do eat meat.  My advice to you, from a practicing buddhist, is to read up on basic buddhism, and ask alot of questions on things you do not understand.  If you can get a chance to visit a buddhist temple, I highly recomend it, as most of the monks and nuns are more than willing to sit down and talk with you about such as well as tell you about their particular path or sect.  And if you can attend a celebration or 2, definately go, as it is different, but think carefully on what you are wanting.

Hey there and welcome to the board!

Those are very good points. 

Let's be clear, though, that Tibetan Buddhism isn't entirely Vajrayana.  Since the Dharma lineages of Tibet include Sutric teachings as well, one can practice Tibetan Buddhist teachings (not different from other Mahayana teachings, of course) without practicing tantra at all, even if you keep the tantric view in mind.

That said, it's very recommendable to have a teacher in any tradition. 

LozangK
Beliefnet Host, Buddhist Teens

I disagree with the notion that Sutric teachings are somehow underdeveloped in theTibetan schools and that the Sutric systems are regarded as inferior.  Tantra is essentially seen as the most preferable path for those of a predisposition suitable for its practice.  If one is a serious practitioner of tantra, then the sutric teachings are certiainly considered preliminary, but since they are necessary they could hardly be called inferior. 

Most lamas don't give abhisheka for highest yoga tantra frequently.  I've been studying Tibetan Buddhism for about six years now, and I can say that whenever the chance to recieve that kind of empwerment comes up, it is not often, and is usually something only reasonably experienced students take advantage of.  Empowerments for the "lower" classes of tantra are more frequent, but even then one is expected to keep samaya, which is not taken lightly.   You spend much, much more time studying texts from the Stages of the Path (lamrim) genre, which is almost entirely sutric.  Even great lamas will spend a number of years meditating in retreat on the Stages of the Path in order to develop renunciation, bodhicitta, and sunyata before moving on to tantra. 

There may be some confusion or suspicion about the Tibetan attitude towards sutric Mahayana schools, especially Chan, perhaps stemming from master Hua Shang's expulsion from Tibet.  But one must remember that that happened centuries ago, and I have never heard or read any disparaging comments regarding Chan in any Tibetan texts or teachings.