Should I just save up for a new computer?

My mom get a used PC from a friend and is giving it to me. I game a lot, and need a computer with a pretty nice video card. The PC my mom got is a Dell dimension, not sure which one it is I think its the 2400. The thing is I need a new video card, but this PC only has a regular PCI slot, not a PCI express….what should I do?