It may well be that the OP can indeed install Snow Leopard. I recently installed SL on a Core2Duo iMac (an Intel Mac rather than PowerPC) running 10.4.
To the OP: What Mac do you use? If you're not sure whether it's PowerPC or Intel, click on the Apple icon in the menu bar at top of the screen. It'll show you what sort of processor your computer uses: PowerPC or Intel. If it's the latter, you can install Snow Leopard on it.