3 pesky troubles

These are just weird things happening. I've just been guided through getting the pc cleaned from viruses and spyware, and it still shows clean, but here's what's going on now:

1. My computer says I'm not using a valid product key to install Office 2003. This is the correct key that was on the package and it worked before on my previous computer. The hard drive I'm trying to put it on used to have Office 2000 installed but it was reformatted.

2. When I try to backup Quicken 98, the computer tells me the disk is full. It's a 60 gig with 47 gig free, I checked.

3. Whoever had this pc before put 6 gig into c: drive for the OS (XP). So programs are d: drive, and some programs are trying to install into c: drive and won't give me a chance to redirect the installation (Sun Java, for instance). Plus it's confusing to have a d: as the main drive when I've used c: ever since my first PC (which had 16meg on the mother board, ha ha). Isn't there a way to rename those drives, and if so is it wise to do so?

thanks for any ideas ...