First: for those who are recommending one use Wubi to install: don't. Please don't.
Non-Ubuntu Linux forums are filled with people looking for help after Wubi screwed up their Windows installation and now they can't boot into one or either of the OSes.
There is no practical need for WUBI (as those recommending playing with Linux in a virtual machine rightly demonstrate). It runs the risk of leaving you unbootable and also gives you a more limited Linux experience. If you're going to actually install Linux, please do a normal, regular install of the OS - you'll be safer in the long run.
Secondly, for those who are lifelong Windows users and want to check out Linux - it might not be popular to say, but you might not want to choose Ubuntu. Ubuntu has a controversial new user interface that seems more intended for touch displays and ultra-dumbed-down applications than normal desktop use. You don't really want to add an extra learning curve to the mix. You'd probably be much more comfortable with a distro that uses KDE as its default desktop interface since it uses the standard, normal taskbar/"start" menu type interface you're familiar with. You could probably sit down at a desktop using KDE and not realize for a long time you're not using Windows 7. If you make the switch to Linux then later on, once you're comfortable with the "linux" part, you can investigate other desktops and see if you want to switch to one of them.
Third, for the original poster, provided Linux doesn't have any trouble with your particular hardware, you'll find performance much better going to Linux from XP with your specifications. I have an old laptop with a 1.8GHZ single core 32bit Sempron chip with 512MB of memory and an unbelievably slow, 4200rpm (!) IDE 75GB hard drive. XP loves to use the page file to swap things out to disk. Given that the disk drive in this laptop is incredibly slow this would cause the machine to essentially pause quite often as it swapped memory data out to disk or read it back in, even when there was free memory. Linux normally only uses the swap file when memory is close to filled up, so that alone made the performance much better for me when I replaced XP with Linux on it. Linux, like more modern Windows versions, will use all free memory to cache hard drive writes/reads and leave recently used files in memory. XP doesn't really do this and the performance boost was again quite noticeable. I'm able to run the latest version of OpenSUSE Linux with the full KDE desktop on this laptop, so you should be able to run any linux distro you're interested in on yours. You will definitely see a major boost in performance if coming from XP or having low memory, and like me, you qualify on both of those. Linux also uses much less disk space - a default install of OpenSUSE only averages about 3GB, and that's including office suite, image editing program, browser, e-mail, instant messaging, VoIP, PDF reader, etc.!