I recently came to know about Tai chi and I'm interested in learning it. Unfortunately, there are no Tai chi classes around. Can I learn it through internet or any other medium? If so please guide me.
I would agree with the others - find a reputable instructor near your area if at all possible.
If you truly can't find anyone in your area, Richard Clear has produced a number of DVDs. Thought I can't personally vouch for the DVDs, I attended one of his seminars, and my instructor routinely praises Mr. Clear's work in spreading the word about tai chi chuan, Hsing-i chuan and internal arts in general.
You're probably wrong about not being able to find Tai Chi. You probably just don't know where to look. Google is a skill ;) Make sure your google-fu is strong. Tai Chi is a very popular martial art and it is taught in a lot of places. Check your local gym or fitness club.
Don't try learning Tai Chi from the internet. There are too many subtleties. You need a teacher there to correct your posture for every slight mistake. If you honestly can't learn Tai Chi from a qualified instructor, learn something else from a qualified instructor. This will at least give you the balance and gross body movements that will aid you in learning Tai Chi later on when/if it becomes available.
Finding a good instructor is a whole different topic, which I won't address, since that's not what you asked. I did, however, want to make sure to throw this advice in: learn what to look for in a qualified instructor.
I know the temptation is strong to ignore this advice and learn from the internet/DVDs, but you'll only be wasting your time. You could find yourself having practiced what you thought is Tai Chi for years, only to realize you have no idea what Tai Chi is when you come into contact with a real Tai Chi person.