Welcome to LQ.
Not to give Emerson a hard time, but Lubuntu is a good recommendation for older boxes. I just surplussed an older laptop to Second Son. I installed Mint, then installed the LXDE desktop (that's the "L" in Lubuntu) for his use, as he now is officially a Linux Newb.
The distro is not the most significant issue, the desktop is. Some desktops suck up lots of resources; others require very little.
There was a fellow at my LUG tonight demonstrating Crunchbang, which he is running on an old Thinkpad with a Pentium M chip and two GB of RAMs.
There are a number of recent LQ threads from XP users considering migrating to Linux. You might use the search feature to find some of them and read the responses. Another thing you can do is burn Live CD's of distros you are interested in, boot the computer to the CD (warning: it will be slower than a boot from the hard drive), and explore them. That will help you pick something to your liking.
Could you tell us more about your computer, particular the processor and the RAM? That will help persons make useful suggestions.
Linux is not hard, but it is different. Expect it to be different, don't expect it to act like Windows, and you can be a Linux user in no time.
Last edited by frankbell; 04-03-2014 at 11:14 PM.