It sounds like you have a pagefile which is out of control.
Unless you're doing a lot of photo editing, a pagefile of 2.63 GB is overkill!
Unfortunately, I don't know where the setting is in XP, but I'm sure some other member can tell you.
And just to check something, go to your D drive, select all, and then right-click for the properties of all the files and folders.
You'll be getting 2 numbers. One is Size and the other is Size on disk. Are there any big differences between the two?
If yes, a defrag might help you recover some of that space, but how much I can't tell you.