What OS X 10.6 Snow Leopard disk are you using? A retail disk, an upgrade disk, or a gray-faced disk from another mac system? If the latter, it won't, as you've found out, install, as they system disks that are delivered with Apple systems are locked to that system type. So if you have one from an iMac, for example, you can't use it to install on your MacBook. If that's the issue, buy a retail version from the Apple online store.
Do you have less than 1GB of memory? That would hose the installation too.
I take it you can boot from the SL installer? On the second screen of the installation process - right after the language selection - you have access to Utilities in the Menu bar. Get to Disc Utility and check the hard drive - verify, repair, etc. If you have a complete back up, I would recommend erasing and reformating the drive before proceeding with the OS installation.