Your specs are good enough to run most of the major distributions without a hitch, but I would recommend that you use Ubuntu because of its easy set-up, uncomplicated package management, and massive userbase. This provides a large number of easy-to-install packages, a large and helpful support forum, and the like.
Also, I would recommend using the GNOME desktop environment, as it is less resource-intensive than KDE. If you want something even more lightweight, you can run Ubuntu with Fluxbox, XFCE, or a number of other lightweight desktop environments. The instructions of how to do this are on the Ubuntu forums, which can be found at www.ubuntuforums.org
However, Ubuntu with GNOME is the easiest and least-complicated way to get you squarely into Linux computing.