Phantom Disk Usage

I have a 80GB physical drive partitioned into two logical drives – 20GB and 60GB. My 60GB drive has only 17GB of data on it (counting hidden and system files). However, XP thinks the drive is full (only 1% free space). I don’t have a pagefile on this drive (its only a data drive) and can’t think of anything else that would be hogging the space. I’m running Norton Pro 2003 and it hasn’t found a virus. Anyone have a suggestion???