What program for overclocking a GTX 260?

Ok so I used Riva flawlessly on my 9800GTX. But with this new GTX 260 I got from my friend it's having all sorts of issues. First of all fresh drivers are installed as well as reinstalled a fresh copy of Riva. The things I'm having issues with:

- Everytime I start riva it says my video driver is not compatible with the current version of riva. I think I'm using 2.24C or whichever the website has.

- Second under the hardware monitor all the clocks and everything are all crazy and go up and down every few seconds.

The odd thing is under the settings everything shows the correct values 576mhz, 2000mhz shader, etc.... Also the Precision does the same thing.

Has the card been overclocked before? What distributor is the 260 under (eVGA, Asus, etc)? Have you removed the old 9800GTX drivers? Have you wiped your RIVA profile for the new card? The GTX260 tends to throttle its clocks by <66% while idol. Have you tested the numbers while under a load, like in a game yet?

Alot of times the latest drivers are newer than the latest RivaTuner.
You can force the card to run at Performance 3D mode all the time, its on the same screen where you OC the card.
This will force the card not to downclock while idle.

Does anyone know how you can unlock the "force constant performance level?" Mine is greyed out.

Could be the card or the driver causing it to be greyed out.