Assuming I'm a beginner with an obnoxious comment like that (belied by my previous post showing that I do know my way around Windows), does not "make me think". I know my system: it is a virtually untouched, 2-month-old, default install of Vista Ultimate. No extras, no Norton or other virus/spyrware/adware protection of any kind, a handful of very old, mid-1990s-era art programs needed for legacy purposes, none of which take up much space or have ever exhibited disk space-gobbling behavior, the downloaded Windows Live Mail program, and otherwise just the default installation of standard Vista stuff like IE. And if you were listening, I said I had already made sure that hidden and system files were visible. Are you saying one of my ancient art programs has uncharacteristically decided to start making files that are super duper EXTRA hidden, so they can't be seen under ANY circumstances?
In any case, this does not explain the .hdd file expansion. Even accepting the mysterious extra 3GB as some weird Vista quirk, the C:\ drive is still, at its greatest, only 14GB.. not 21GB. It has never *been* reported anywhere near that high, using either of the methods I described above. And when compressed, the extra 7GB in the .hdd disappears. This has got to be a Parallels thing.