[uxevangelist]

Try this on for size, assuming you're starting from a clean HDD:

1 - Pop in your XP installation disk, create 2 new partitions and go ahead with installing XP on one of them.

2 - When XP finishes installing, pop in your Vista installation disk and install on the 2nd partition you created.

When Vista finishes installing and your system goes to boot, it will ask you which version you want to boot in to. Unless you want to choose a different OS to default to, you're done. =) Now, if you're starting with either Vista or XP already installed, you will need to create a new partition within your installed OS, then install the other OS of your choice to that partition. Depending on if you're starting with Vista or XP will determine which process you need to follow to get dual boot up and running. In those cases, the posts above mine have the necessary steps for such procedures.

-Stephen