Be very careful, I've never gotten dual booting to work with Linux and XP.
That being said, there's a ton of "distros" out there, but each cater to a different taste.
I use Gentoo (
http://www.gentoo.org), which is a source based "meta-distro." That means I can pick and choose whatever programs I want installed, compile them from scratch and hopefully optimize them for my computer, and then have an almost completely customized install. It's not really for beginners though, as there's no installer program, just a bunch of commands to type (although, they are very well documented). Another feature of Gentoo is the online community, which is the best Linux one I've seen yet (
http://forums.gentoo.org).
Another good distro is Debian, which is similar to Gentoo but more stable and binary based. I believe their site is
http://www.debian.org.
I think that it really depends on how much you want to learn. With Gentoo, I've taught myself much more about Linux than anything else, with other ones like Debian or Redhat, I had a working system, but no knowledge on how it works.
http://www.distrowatch.com
That website should be a good website to look at different distros, and figure out which is best for you. Narrow it down to a few, and then try them all out if you have the time. Nothing beats actually playing with a distro and learning how to use it.