MacBook Pro running Tiger 10.4 erase start up disk I do not have the original disks but the computer has been upgraded to Snow Leopard.  I have the Snow Leopard 10.6.3 disks but the computer will not allow the disks access to my startup disk.  I need to erase all and restore the computer to its original state so I can sell it. I have talked to Apple and they say the machine is too old and they do not have the original disks available.
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.