You can see the disk layout in the Windows Disk Manager tool.

One reason the "C" drive appears to under report it's size could be that it has a recovery partition on it. If you are running Win 7, there are a couple of hidden partitions used by the OS.

You could go the easy route and just add an external HD if you have a port available.

I already have an external drive scook, just for file-project storage. I like to run and keep ongoing projects on the same drive, it cut's a bit of latency in processing. I'm going to work on the switch some more later this week. While I struggle with temptation over getting a newer DAW. It's amazing how fast things get obsolete in the tech world. Is art tying to catch up to tecnology?, or is tecnology trieing to catch up to art?