Yes, you can score in the neighborhood of 90 percentile with one month of preparation. If I were you I'd do the following ASAP:
1. Get "Cracking the GRE Mathematics Subject Test, 4th Edition," By The Princeton Review from Amazon.com
2. Read linearly from the first page to the last, taking notes, and checking the Wikipedia pages on important topics (such as continuity, uniform continuity, compact spaces, etc.), as you go along. Don't do the practice sets in the "first pass." just focus on getting acquainted with the material. The "first pass" should taken no more than one week.
3. Do the "second pass" in the following week, but this time do it intensively.
4. The third and the fourth week should be devoted to doing all the problem sets in the "Cracking" book, and also the four released GRE tests (link available in this forum somewhere). You may have to spend upto 5 hours a day in the final two weeks to ensure that you land in the 90+ percentile.
5. Keep a log of errors, and be mindful enough not to make stupid errors.
6. The actual tests resemble the released tests (the Cracking tests are harder), so don't be scared, just keep on practicing: speed and computational accuracy will both be of paramount importance: so try to be sharp and focused while practicing. The "cracking" book gives you most of the tools, and the remaining tools come from Wiki and textbooks.
7. You are extremely likely to score at least in the 85th percentile, and possibly in the 90 percentile neighborhood, if you do 1 to 6 with the belief that you are indeed going to "Crack" the GRE. Fear is your enemy.
Good luck to you.