XP supports this to an extent in Administrative Tools, Computer Management, Disk Management (e.g. you should be able to remove the D partition and then expand the C partition - although I'm not sure if you can do such operations on the system partition). Load up Computer Management and read the Help.
Alternative is proper partition manangement software like Partition Magic, which will certainly do it.
Or if you have Acronis True Image, you could delete teh D partition (as above) and restore an image of C taking up more of the available space.