A7M266 with AMD athlon XP 1600+

Okay... i set my speed in bios to 1400.. which is the highest setting for my processor .. and the other option is 1050.. but its supposed to run at 1400.. so i install windows 98.. it works fine, i install the winXP upgrade, and it WILL NOT install at 1400.. i had to set it down to 1050, so after it installed, and i did all the drivers, i tried to set it back to 1400... it worked for a few minutes after windows loaded, then it would just reset.. and then do it immediatly after it loaded, or while it loaded.. but it will work fine if i put it back to 1050.. how do i make it run at 1400 in xp? i don't understand...