HD thinks it is full??

Here is my problem. I have a 220 GB HD and about 100GB of data on it (including the OS).

For some reason, Vista thinks the HD is full and tells me I have only 10 GB left.

If I go and delete 30GB, it will tell look like the space is free, but then in several hours, it will be full again.

I don't have anything else to delete and there is definatly not that much data on the drive.

This is also slowing down my computer.

I have Kapersky antivirus 2009 and it is uptodate and not detecting any virus's or spyware.

I called Dell and they told me it is a software issue.

I went into MSCONFIG and disabled everything except system programs and the problem is still there.

Any suggestions? Is this a software/ malware issue or could it be the HD is bad?

System restore is turned off.

Using a directory tree program shows that there is only about 100GB of data on the drive as well.
Thank you

SYSTEM:
Dell XPS 1530
Core 2 2.2
3 Gigs memory
250 GB HD
Vista SP1 32bit
Kapersky Internet Security V2009