The best tip I have for anyone studying for the ASTB is to keep in mind that the military has proven through research that those who score high tend to do well. They do use your scores as a determinate factor.
Use your time to study every possible resource from the military gouges, arco study books, aviation books, etc.
If your determined to ask questions about what your chances are check out the the "Navy OCS" forums for the different boards where people post their ASTB scores, GPAs etc and whether they got pro rec'd. The most recent will be September and October 2009 Board results.
Find a mentor or someone you can talk to who is or was an officer. Mine is a former EOD LTCDR.
My Stats: 25yr old female; ASTB 8/9/9/62 (up from 5/5/5/50); BS Recreation & Tourism Mgmt 3.4 GPA; Active leader in a student organization; Recommendation letters from 2 retired military officers (USMC & USN)
Pro-rec'd for Pilot/SWO/NFO, Oct '09 Boards.
**I had no prior aviation experience or knowledge prior to studying for the ASTB, just sheer determination.