If you have an external usb hard drive or a USB Pen Flash Drive you could move some of your personal My Docs Files and pictures to it. That would stop the low disc space warnings.
Have you emptied the Recycle Bin? and the Temp Folders? etc
If XP click on Start, Run, and type in: %Temp% and then press OK. That will open Temp folder and you can safely delete everything in there. Click on a blank part in the righthand pane then hold down Ctrl and press A ('a' not capital A) that will select all and then you can press Delete.
There might be some stubborn ones that won't delete. Don't worry about them just delete the ones that will.