Sounds like a load of now empty temp install folders are chewing up drive space where you need a drive cleaning tool. One freeware good for that is called CCleaner found at
http://www.ccleaner.com/
Memory and drive space only connect when the lack of drive space cramps that required for the paging file used for virtual memory. With XP that's abouit 2gb of drive space reserved. Besides cleaning up useless files and folders the drive may have become heavily fragmented from a large change of programs along with the manual deletion of things.
The system registry is another item that sees an accumilation of now useless entries when uninstallers leave things behind still trying to load drivers no longer on the drive. Eusing software offers a free cleaner that seems to perform well in that area.
http://www.eusing.com/free_registry_cleaner/registry_cleaner.htm