4GB freed suddenly

[vee_ess]

I have 4 partitions on my HD, one of which is 15GB. That is the primary partition, my C: drive, which I use probably 90% of the time. Well I filled it up almost completely; 200 megs left. So to clear it out for now, I moved an ISO to another partition(648MB), and deleted Java 2 RE (200MB) and application that used it (40MB).

I add up the amounts as I go thinking I have about 1GB free now.
200MB + 650MB + 200MB + 40MB = about 1.1GB...

I go to defrag and it says that I have 5.02GB free space on my C: drive. I think defrag.exe must be corrupt so I check it at My Computer and that also says 5GB free. I have a lot of important stuff on here that I can't lose so I'm starting to worry.

So I have 2 questions...
1. Any one have any ideas of how I got 4GB from seemingly no where?
2. Is there a log of all the files deleted?