I'm using Ubuntu 5.04, and even managed to get it to drive both of my monitors at the same time!
My machine is a Dell Dimension 4500, which had been running only Windows XP. Ubuntu let me set up a partition on the hard drive for Linux, and at startup Grub asks which operating system I'd like to boot into.
Making enough free space on the hard drive was a bit of a challenge because the XP disk defragmenter (and even the commercial Diskeeper defragmenter I used as well) didn't move all the data to one end of the hard drive. But I found a marvelous command-line utility that did just that: it's called DIRMS.exe (which the author says stands for "Do It Right, Micro Soft)."