MacBook Pro running Tiger 10.4 erase start up disk
If the disks you have are not full retail disks [grey background rather than white, quite often], then they may not work on all machines, but only those they were designed for at the time.

Apple still sell the Snow Leopard DVD - http://store.apple.com/us/product/MC573Z/A/mac-os-x-106-snow-leopard - though whether it's really worth $19 these days is debatable.

If you know anyone with an Apple Developer account, Snow Leopard is available as a disk image, directly downloadable from Download Mac OS X 10.6 10a432 DVD image (direct link from Apple), for burning to DVD.