can i erase C: without erasing OS?

[njunja]

So, i'm running Vista, can i erase C drive with OS intact or even keeping the programs i select from being erased?

 

[Joel]

Not possible: programs can't tell whether it's an OS file or a user file. You'll have to erase the entire drive and reinstall Windows on top of it.

But if you're just wanting to erase unused disk space, Eraser can do that.