Another vote for Ubuntu. I've used several distro's over the years and Ubuntu beats them all, in my opinion. I still run old hardware, a 10 yr old self-built AMD based system with 1.5gb RAM and 80gb HDD. Using Ubuntu 8.04 LTS on it. It's solid as a rock and runs flawlessly. I log with xLog and do digital with FLdigi.
Dell Inspiron 1525 laptop runs Lucid (10.04.1 LTS).
Most certainly NOT knocking Fedora (another great distro) as I've used it, as well as Mandrake (now Mandriva) and I tried Suse (didn't like). I like Ubuntu best because of the support community. Have a prob? Hit the forums or the IRC channels. Get answers/solutions pretty quick.
Ubuntu and Fedora both have lot of ham related programs.
Whichever you choose, they all have their fans and will try to sway you in their direction. Like a previous poster suggested, try a few different distros and see which one you like best. Doesn't cost a thing except some time
BTW: I still have a Winders XP Pro drive around...just don't remember the last time I had to use it.