to overclock your video card with powerstrip:
after you install powerstrip, you'll see the monitor icon in your system tray, right click on it, select the submenu "Advanced" or something like that, then select performance.
there should be 2 sliders (sometimes there's might be one, or so i've heard), one for Core Timer speed and one for Memory (i forget the acual terminology). Take not of what they're set on in MHz, you'll need it in case your video card bugs out sometime after overclocking.
slide the two sliders gradually up and test your new settings by rebooting and running a 3d game of somekind (Q3 Arena, UT, or Q2 all work). Keep moving the sliders up each time until either your video card craps out and crashes your system or you reach the limit on the sliders.
BEWARE: OVERCLOCKING CAUSES SERIOUS HEAT ON SOME CARDS SO MAKE SURE YOU HAVE SOME METHOD OF COOLING ON YOUR CARD WHETHER OR NOT YOU HAVE A HEATSINK AND FAN ON THE CARD (For me, leaving my case lid off and pointing a deskfan in to circulate air works fine).
Also note that you can seriously damage your equipment if you let the card get too hot. Search the internet for info or tutorials on your specific card to see what other people have found works. Try a Yahoo! search with +"{your video card}" +overclock (or +review, sometimes the reviewers overclock their cards).
Good luck!