Hi bschoolhunter,
To start, it would help if you had a list of Schools/Programs that interested you. In that way, you could research the individual Programs to confirm whether they accept both the GMAT and GRE or just the GMAT. If you're not sure which Schools you want to apply to just yet, then that's fine - all things being equal, you should study for the GMAT (since that Exam's result is the 'standard' that Business Schools accept as part of the application process.
Since it sounds like you're just beginning your studies, then it would be a good idea to take a FULL-LENGTH practice CAT Test; you can download 2 for free from
www.mba.com (and they come with some additional practice materials). If you want to do a little studying first, so that you can familiarize yourself with the basic content and question types, then that's okay - but you shouldn't wait too long to take that initial CAT. That score will give us a good sense of your natural strengths and weaknesses and will help provide a basis for comparison as you continue to study. A FULL CAT takes about 4 hours to complete, so make sure that you've set aside enough time to take it in one sitting. Once you have those scores, you should report back here and we can come up with a study plan.
I'd like to know a bit more about your timeline and goals:
1) What is your goal score?
2) When are you planning to apply to Business School?
GMAT assassins aren't born, they're made,
Rich