Your video card won't be affected I don't believe.
Overclocking the processor is more likely to affect your RAM voltages/timings, and also maybe motherboard speeds also relating to the processor.
Overclocking the FSB will for instance increase the speed of the CPU, but along with that to get more, you may need to increase the voltage, if the standard voltage isn't giving enough power for the overclock.
Always be careful when overclocking though. Too much of an increase can easily damage your system. Usually by it frying, because not enough cooling has been achieved...
Check this thread out which may help you:
I hope this helps