If you install Ubuntu, it will add it's own bootloader, and most likely, add both Vista and XP to the list. And yeah, you can run 3+ os fine. I got 2 on my laptop, and might install Ubuntu, if I can be ****ed to get rid of some of my Star Trek episodes.
Wonder if anyone ever booted XP, Vista, Ubuntu, Fedora, Tiger, and Leopard on the same PC.