Linux. There are a half dozen variants of it (called distributions) - Red Hat, Debian, Mandrake, etc. Other than that, there aren't any mainstream operating systems for the x86 Intel architecture.
Good luck with it.
This is my third day on the phone with Microsoft (i'm on now, on hold of course) I want to remove Windows XP Pro from 2 computers and Windows XP Pro media center from 1 computer. What can i use as for and OS that would work well. Thank you