|Nope, didn't see 0.5G mentioned.|
There are a few ways to delete obstinate files.
Firstly try it in Safe Mode (F8 while booting then select Safe Mode).
Secondly there are small free programs around such as "Move on Boot" which
delete files next time you boot up.
Last resort would be to get a Live Linux CD (such as Puppy Linux) then use the "burn an image" feature in your CD burner to create a CD. You have to ensure that the CD is ahead of the C drive in BIOS, then boot to Linux with the CD in the drive. When it has booted up, at the bottom of the screen (in Puppy) you can view the CD drive and delete the files. The CD just works with RAM so nothing else will get touched and Windows will be back when you boot without the CD. Note that Puppy might make a file and folder on the root of C for data.
The last two suggestions will not delete to the bin so once you've deleted the files they will be tricky to recover. I can't really see why deleting them should cause any issues but I have to make it "your risk". Start with the oldest ones.
Always pop back and let us know the outcome - thanks