I'm not sure about temp program but here is the way to safely overclock your video card.
Start with either your memory or core frequency and increase slowly (a few MHz at a time) then run a 3d program such as 3dmark 2003 and check for artifacts.
Keep on increasing until you see artifacts (display corruption) and then take it a few MHz down until you obtain a stable frequency.
Do the same thing with the other frequency and voilĂ*, you've O/C your card to its maximum stable frequencies. If after playing for a while you start seeing artifacts again, just take your fr. down a bit again.
My gaming machine:
P4 2.8 GHz
2 X 512 MHz PC3200 in dual DDR mode
Intel D865PERL MOBO
integrated 6.1 MAX audio
Logitech duo MX mouse and KB
ATI RADEON 9800 PRO