So if both computers are on the same network in the same house, and the computer you want to access has windows xp on it,
why can't you just open my computer, right click on the c drive, click sharing and security, and then share it, and check the box beside "allow network users to change my files"
Doesn't need a password if you have simple sharing on, and sure it isn't a good idea to do that security wise, but hey, you have had your current setup for a while now and haven't had a problems with people breaking into your network have you? So how is it different just because you are sharing your entire c drive?
I may be missing something here, but that is what I would do.