boot up while holding the DELETE key.
select first category in bios.
go down to the 'front side bus" item, select 'user define', enter 115. you can go higher if your computer is stable. Find Prime95 on google.com and download it. run prime95 'torture' for 4 hours should be enough at this low fsb speed.
your 1.6a should do 133 fsb easily. after you hit 133mhz fsb, you should run Prime95 longer.... maybe 10 hours..
If you haven't installed the Abit software, do it. Install Hardware Doctor from your CD. While you are using Prime 95, run Hardware Doctor to monitor your cpu temperature. You don't want your cpu temperature above the high 50's Celcius.