overclocking is dependant on the Mobo.
If you have a crappy mobo, you wont be able to overclock.
Basically if you look in your bios, and see options to adjust FSB, Dram:FSB, and stuff like that, you can overclock.
If you dont, it may be hidden, or just plain not there.
Now adays on newer boards you can overclock through the operating system via some software, but again it relies on the Mobo, if the mobo doesnt support overclocking then you certainly wont be able to do it via some software.
Graphics cards on the otherhand you OC them through software. They are not dependant on the mobo. Mobos control themselves (FSB, PCI), Ram & CPU frequencies.
If you are new to overclocking read up and ask questions or you can easily break something. There are plenty of safe things to play with though, just need to understand what they are.
You can build yourself a decent gaming PC these days for about 500 excluding monitor and perhiprials. If you can reuse some parts like case, PSU, & HDD your looking at 250~400 for a budget gaming PC.