C: vs D:

Margie’s hard drive at home is divided between C: and D:. Everything, of course, is installed on C:, and copying over a 900Mb CoH installation Zip file probably didn’t help things any. So the question came up of how to easily shift things between C: and D: without un/reinstalling various applications (bleah).
The three ideas (here described for WinXP Pro) came to mind. Best to have all apps closed during this:

1. Do a Disk Cleanup. This is in the Start menu under Accessories / System Tools / Disk Cleanup. If there’s old installation files, unused temp files, etc., lurking around out there, this is the place to easily clean them up. Doing a defrag afterwards wouldn’t be out of place. (Margie had already done this.)
2. Move the swap file over. Under Control Panel / System / Advanced / (Performance) Settings / Advanced / (Virtual Memory) Change. Use this screen to add a paging space on D: and eliminate or minimize the paging space on C:. There may be restarts involved, or multiple iterations to do so (hard to tell, since it turned out that this had already been done on her machine during a previous space crunch; I took advantage to add a large custom size to support upcoming CoH play). (Official MS KB article here.)
3. Move My Documents over to another drive. Right-click My Documents (off the desktop or the Start menu), then choose Properties / Target. That will show you the current target folder set for your account as the My Documents folder. Click Move …, then choose where you want it to be (e.g., in D:\, creating a new folder called My Documents there). Accept, and Windows will ask if you want to move the contents over there, too. Yup, you probably do. (More info here and here.)

FYI.
In theory, you could some (or, more easily, all) the applications under C:\Program Files to D:\ by doing the move and then tweaking the registry, but, damn, that sounds like asking for trouble.