I am using a 2008 MBP running 10.6.8 and I knew I had ~50 gigs of space left. A window popped up telling me my startup disk was out of space. I clicked on finder. It said "Zero KB available" and then the number kept changing. A few gigs, then back to zero, and then it made it's way back up and stabilized at 49.12 gigs. Whats up? Virus? HD failing?