you can overclock the video card using a program called Rivatuner - can be found at www.guru3d.com
you can do the following tweaks:
disable unnecessary services in "services.msc" (type that in start, run) - some of them you do need
disable startup items in "msconfig" (type that in start, run)
disable system restore
disable the XP theme and extra animations
disable "automatically search for network folders and printers" in My Computer > tools > folder options > view
that speeds up browsing files
if you raised the FSB to 200 (DDR400), then you have overclocked it.
the FSB and the multiplier make the CPU speed. if your CPU is at 2.8GHZ now with a FSB of 200 (DDR400), its multiplier is 14, because 14 x 200 = 2800MHZ.
normally you can't change the multiplier, but you can change the FSB.