Originally Posted by TaintedSoul

You can image/clone the C onto the D, but you cant merge the two drives. You could move the C's swap file over to the D drive. This will free up some space.

Right click "My Computer" > "Advanced" > "Performance" > "Advanced" > Change

Select D and select system managed size
Slecet C and select no paging file

Reboot.

My XP installs for Media Centre take no more than 2.8Gb without swap on the drive. As a desktop probably about 8GB. You seem to be storing numerous files on the C drive that most likely could be moved. By files I mean, music, videos, large documents, pictures etc.. etc..

Clean out temp folders "c:\windows\temp" or the one located for user within Document Settings.