Quick Computer Question?

Christmas is gonna be here soon, i want a new video card. so do i have PCI, AGP, or PCI Express? Its an Evo D510 SFF, Pentium 4 processor (2.4 ghz), 40 gig hard drive, XP, and 64 mb video card in it now. I plan to upgrade someday in the future. Just wondering if its PCI, AGP, or PCI Express. (Cant open it, more like really wont. is there software which can detect it?)