May I know how eligiblty for GRE and what are the prearation needed in that?

Anyone can take GRE CAT, there are no restrictions on age or qualifications. The test score is valid for five years, but for admission,it is better if the score is recent( 2 years).

Helpful Books:

1. Barron's GRE ( quantitative & verbal)
2.Nova GRE ( quantitative & verbal)
3. Word Smart ( word lists if you want to go beyond barron's)
4. kaplan Math work book(good chapters on maths)
5.Big Book (27 tests)
6. Arco GRE-( answers to the real essay questions)- the pool of issue and Argument topics fully discussed.

Some Web Links:

majortests.com : Practice tests and information for high school, college and graduate tests

TestMagic Test Prep

ETS Home

Number2.com :: Free Online Test Prep


Just Google , you will find numerous sites which have word lists, practice exams and GRE practice software.