I'm kind of a control freak about where programs install and always want to know where it's going. But that's just me and I'm kind of compulsive about it.....
Anyway, this is the first thing I found that seemed to suit the problem. It's a simple registry edit in XP. If you're worried about messing up (believe me, I understand) then you can export your original registry to save it using regedit and restore it if you need to, or you can use system restore.
I hope this is what you're talking about.....
http://www.winguides.com/registry/display.php/1137/
I think if you simply change the "C:blahblahblah" on under the "value data" keys to "D:blahblahblah" it'll do what you want.
Good Luck
