What type of Snow Leopard disc do you have? If your mac originally came with Tiger pre-installed then you will need the Retail Snow Leopard disc.
Read through this Apple article:
Mac OS X 10.4, 10.5: About installation options
Here are another couple of good links to read through:
Leopard How-to: Clean install
How to format my Mac and install Snow Leopard from scratch?
As you probably know, you can go straight from Tiger to Snow Leopard ... leap-frogging over Leopard.
So just make sure you have a good back-up of your important files, photos, music, docs etc.
If you need anymore help, just return here and I'll keep a watch on this thread.
Cheers,
Marty