I'll just throw this out there.....
The very "low-tech" solution is to uninstall some software off of C: and reinstall it on one of the other patitions (looks like D: is under-utilized). I had to do that on my W2k SBS because the C: was originally partitioned at 10GB (don't get me started... it was before I got here) and was hovering at 10% free space. I didn't feel comofortable trying any kind of partitioning software, so I just moved software to the other partition. Now I just routinely run a cleaning program to remove temp files and I'm able to keep it at 20% free space.
I'm sure there are other G2Gers who can give additional (and maybe better) advice..... it' won't hurt my feelings