I woulg galdly lend you a HDD if I had one and lived near you hehe, but unfortunetly I do not qualify for either of these.
Heard of Partition Magic? Got it?
If you have it or can get access to it (preferaebly v7.0 or v8.0 as I havent used any of the earlier version and it may not have the features that you need) install it on your machine.
With this (must have) program you can create another partition (in your case around 40GB should be more than enough) and you can move the files you dont want to lose onto this new partition.
Then you can format c: and reinstall as you need with all the data backed up on to (assumably) d:
After the reinstallation you can either leave it as is so you can always have a 2nd partition or else Partition Magic also has a 'Merge Partiton' function that will.... merge... them back together again.
No doubt that there maybe other programs that could do the same thing but from personal experience I would reccomend Partition Magic as this process is quite dramatic and one small mistake can cost you 35GB of important things
Windows XP Pro 2002 (SP2)
Intel Northwood 2.4GHz
Compaq Evo D510 SFF
768MB DDR PC2100
NVIDIA TNT2 32MB
Intel 82801 (AC\'97)
C: 40GB (FAT32)