Never seen that
Anyway, one thing to try would be to b
oot from the Vista DVD and click 'Repair my Computer'.
At the prompt to select your OS, click on the button 'Load Drivers', it should appear an explorer-style drive browser.
Right-click on the drive (C:\) and untick 'Compress this Drive', which should still be ticked on, apply including subfolders/files.
Reboot.
It should take time to perform this action.