Ubuntu. Definitely. I was a Linux noob too and needed a beginner distro. Ubuntu helps you through many things and stuff, and now I can rely on myself to try fix my own problems as I have understood it so well after 2 weeks.
Download the Live CD from ubuntu.com and try out if you like it. The Live CD also acts as a installer, by click Install on the Live CD desktop. By the way, if you want to keep windows, its really easy to dual boot. I did it using one hard drive, resized the windows partition and stuck Ubuntu onto the space left from the resize operation. It's that easy! If you have any questions, I'm usually on these forums, or add me to msn (in profile) or the ubuntuforums.org