You basicaly set your parts to a higher speed. If you set them to high it can be damaging.
You should increase the clock speed of your graphics card by a few MHz, then run some demanding application like 3DMark or a heavy game for some time, then set it a bit higher and try again. If you get artifacts, strange colors or anything else, set the speed a bit slower. You can stop at any time and reset default settings.
Overclocking the graphics card shouldn't affect other parts, but anything can happen.
TheMajorMMX - Intel P200 MMX @ 225Mhz - V-Tech (PcPartner) Baby-AT mb w/ Intel Triton TX chipset - Nvidia Riva TNT2 M64 w/ 16MB - 256MB M-Tec SDRAM - Still running.....