System memory size?

Is there a way I can find the memory size of a user's pc? Thanks

This would be os specific.
For windows the closest function i can think of would be GetSystemInfo. It fills a structure with pretty much all the info that you see in the system information box.

so what libraries would I need in windows? "windows.h"?

yep
you should probbly have a look on msdn for how it works.