|An 18.6GB primary partition is MORE than enough for your operating system and a few core programs with plenty of room left.|
Just uninstall the programs you have on the C partition and reinstall them elsewhere. You MUST have a ton of programs or you are keeping personal files somewhere besides My Documents. 2GB of total My Documents files is not that much.
My WinXP folder is 3.28GB in size. Subtract that from 18.6GB you have to work with and you have over 15GB of space for a swap file, a few programs that should be on the C drive and the 2GB of My Documents folder.
I suspect you have more than 2GB of personal files or you never empty the recycle bin.
Download CCleaner Slim from the link below. Install to the D partition by changing the drive letter from C to D. Then run both the cleaner and registry modules.