One of the biggest hurdles to newbies interested in Linux is the amount of choice out there. There are literally hundreds of distros, and how are you supposed to know which one is the right one? Once you've taken the plunge and found a distro you like it becomes obvious that the wide range of choice is in fact a good thing, but until then it's somewhat daunting.
aysiu writes some good articles on this subject. In this one:
http://www.psychocats.net/essays/linuxcomparison.php he compares the top three distros on distrowatch.com. He writes from the point of view of a newbie, because he is a newbie himself. You might find it a helpful read.
One thing I would point out is that since you are using quite old hardware, you might find both the two major desktop environments KDE and GNOME to be somewhat sluggish, although they have both received some performance enhancements in recent months. It might be worth considering using a lightweight window manager. I'd suggest XFCE as it provides plenty of GUI configuration tools but has a small memory footprint. Then again you might find that with some of the eyecandy turned off, KDE or GNOME might run acceptably.