OK i want to upgrade my graphics card, but i have a problem?

Ok i have a Sony PCV-RS246 and i won't to upgrade the graphics card. The original graphics card is in AGP slot, how ever AGP graphics are a bit expensive for what i want, However the computer does have 2 free PCI slots. Can i put a graphics card in one of those- and it will still work?, and could it be an PCI express one? What's the difference between PCI and PCI Express?