Vista - Troubleshooting a disk full issue in Vista

I have a fairly new PC running Vista Ultimate. Last week I noticed tha
tthe HD in Computer reported only 3GB of the 137 available on the
primary C: partition of my drive was available. I've been trying a
lot of troubleshooting to figure out what's eating my space

Here's what Vista Disk Manager show: http://i42.tinypic.com/aop743.jpg

Here's what another utility show: http://i39.tinypic.com/2gsoayv.jpg

On the latter, the large, grey area seems to be the issue. THe Lenovo
utility says that it has not scanned that part sue to insufficient
authority (I am the only user and has Admin privileges on this
machine). So how can I go about determining what is eating 74GB of my
harddrive?

Thanks