I agree with Tom on all the points he mentioned. I switched to Fedora Core 4 when my WinXP partition went insane. I just leaped into the deep end and installed FC4 on the entire hard drive (no dual booting, no virtual machines).

It's very tempting to have a windows partition to fall back on, but thats a false economy in my opinion. I can't think of any good reason not to install linux on any machine that will support it (you won't find a machine that won't support linux though I've got a server install of FC4 running happily on a 200Mhz Pentium 1, 64MB RAM, circa 1997. Actually that box originally had Win95 on it and the USB never worked until I put linux on it ).