Dont take this as advice, since I have never tried this in Windows XP...
In Windows XP, cant you just click Start> Run
Type:
diskmgmt.msc
(press ENTER)
and then adjust it from there without loosing data, while the OS is still running?
I have had a lot of bad experiences with partition editing in Linux, and therefor, give it as bad as possible of a name as I can. Still, no matter what, as Dusty said, backing up is crucial. Even if your not partitioning something, backing up can still be beneficial to your computer, its important that in the event of data loss due to a virus, or other system problem, you are able to get back up and running. Many users should consider purchasing an external drive. (I cant say much for myself, I personally dont have one)
(I, for some things, will occasionally use my step dads unsuspecting 180GB HDD via network access when it comes to backups. He never knows... the only problem is the lack of security when going that way about things, if he or someone else found the folder, its not encrypted like it is on my laptop with its wonderful encryption abilities through a wonder program that doesnt happen to be called BitLocker... cant afford to have BitLocker)