OK, hang with me, and we'll see what we can find.
How much space do you have on the hard drive?
HERE is a nice guide for installing Ubuntu 9.04 onto a system which already has Vista. It will dual boot with GRUB, the GRand Unified Bootloader. I think Ubuntu will be in control, with the ability to boot to Vista. If you want Vista to "lead," there are tweaks you can follow.
See what you think. Let us know if you have questions.