Actually I think they may have moved to only computer based tests now for the GRE (at least in the U.S.). I took mine in 2003 and I don't recall getting any choice.
There are some nice things about the computer based test--you can schedule taking it for any time instead of having to do it on a particular day (they way they did the SATs it was always a given Saturday every month or two at 8 am which was the only time they were offered.) I believe you also have a choice after you finish the test of deciding to cancel your scores before you leave the computer. So if you think you've somehow blown it, or got sick in the middle of the test you can essentially make it such that the scores isn't on your record at all. And best of all I think you get to see your verbal and math scores right there at the testing center--no need to wait for weeks for the report to be sent (though you do have to wait for the writing score since a computer can't score that.)
In terms of test prep I think some good stuff is available right from
ETS. I don't remember what else I used to study, but I did teach a Kaplan course on the GRE once. I though the course was not worth the $ at all. But there are some interesting "tricks" about the structure of the test and test-taking itself that might be helpful. You can probably pick up one of their books for $20 or so (you can probably get an edition that is a year or two old a lot cheaper; public libraries often have the older editions too for borrowing.)