Step 1. Repair disk permissions (this is a good idea if you have yet to partition it [go to disk utility, click on OS X partition and hit repair permissions])
Step 2. Open Boot Camp Assistant (Applications->Utilities->Bootcamp Assistant)
Step 3. Choose the size of your partition, partition, put the disk in, click "Start Installation"
Step 4. It should boot automatically off the DVD, if it does not, hit any key when it tells you to. (If you get an error message saying "Select CD Rom" along with a 1 and a 2 with nothing next to them, and your keyboard doesn't work... this requires more work. Recreating the ISO in fact, I had to do this for the RTM version)
Step 5. If it boots from the DVD, make sure you format the partition that's marked "BOOTCAMP" with the Windows Installer. It will make it NTFS automatically (best way to go is NTFS).
Step 6. Hit install after selecting the partition that you just formatted and you're good to go.
Step 7. After installation, put the Snow Leopard disk in (or Leopard) and install the drivers. If you're doing 64-bit and it complains to you, post back here.