Weary about using 3rd party drivers...I understand that, but, give the omega ati drivers a shot..here's a link, make sure you uninstall the old ones first...I'll link you to a program for that as well. If you still have the problem, the omega drivers include an overclocking feature, which you may want to actually try underclocking your card some on both the gpu and the mem.
Omega drivers
http://www.omegadrivers.net/ati/win2k_xp.php
Driver Cleaner
http://www.drivercleaner.net/
Give that a whir, if still nothing...and you still have that old geforce handy, pop that in and see what happens.