Any particular reason you want to keep the raid array?
Raid 0 is problematic when your operating system(s) crash, unless you have a full backup of all data and settings on another drive like a USB external. Because you pretty much have to bring it to professionals or spend a couple months and a lot of money acquiring the right software and learning how to use it in order to recover your data by reconstructing and mounting the raid array with another OS. Unless you have a OEM recovery option where it can reinstall the OS and not lose your data. Most often the manufacturer can supply a floppy or CD iso to boot from to do such a recovery if Vista is hooped.
And if you have Intel Matrix raid controllers, you're probably not gaining anything according to the general consensus online.
I think Vista Ultimate is fast enough for me without Raid 0, but that's just me, and I do have 3.4GHz processor and 4GB of dual channel RAM.
Enough with the parental nag, nag thing.
Now...one question most people will ask is "is this hardware or software raid?". It is important to know what kind of Raid setup you have, and the type of controllers as you may need firmware to use the controllers. Look at section 2.2 of the Debian installation guide --> http://www.debian.org/releases/stabl.../index.html.en
Debian is all open source, free. Proprietary stuff is not included with the installation media, this is the stumbling point when trying to install on existing raid arrays from what I've deduced so far.
If I may suggest...
You can resize the Vista partition through disk management in Administrative tasks in Vista control panel to make room in the raid array for a Linux installation. Ubuntu is based on Debian, I use both Debian and Ubuntu and don't see much of a difference other than it is easy to install proprietary stuff in Ubuntu, and when you go to play a .wmv or .mp3 in Ubuntu, it'll say you don't have the right codecs and offer to intall them, where as Debian usually just chokes and you have to cruise the forums asking why it choked. I've been using Debian for years now, and only recently started using Ubuntu 8.10 and am slowly switching. Ubuntu has an "Alternate CD" available for download, if I remember correctly it is based on Ubuntu 8.04 which will be supported for a longer period of time than Ubuntu 8.10. From what I've read looking for information to post here, the alternate CD will recognize and install on most existing raid arrays.