Dear Ace GRE:
We do not endorse specific products or services, as a matter policy and practice. Just walk into any reputable bookstore wherever you live and you will find many books and aids on GRE. Most books are about the same. Make your own pick.
Computerized centers are all over India, including Delhi, for the General GRE Test. There are many coaching institutes in Delhi that prepare students for GRE computer-based tests. Basically, they train with paper material and make students take practice tests on the computer. Just as with books, we can not recommend a particular service. Just open the newspaper and you will see ads for the training centers. Talk to others who have taken such classes. Do your own research, and do it well!
We highly recommend that you cease asking, or even thinking, the question: "How good a GRE score do I need?" Instead, simply dedicate yourself to doing your best on the GRE. Of course it is worthwhile to find out about requirements for scholarships, but you should not let that influence the level of effort you put into scoring well on the GRE. This test is an important milestone in your life; do your best!
We wish you the best in your test taking.