"Install Windows Vista". yeah yeah I know I know. But I'm serious this time.

I'd like, for the purposes of doing quick diskspace tests, a fast way to create a hugantic ginormous file of the specified size that is ==(available diskspace minus some specific number) big.

Anyone know of a quick way to do that other than doing a crapload of big file copies?

I'm sure there's an internal microsoft tool to do it (or a known way to do it from the command line), but I'm in a situation where I know that you guys could give me an answer quicker than I could find it by asking around here.

Also, I'm aware there's a command to do that sort of thing in Linux, but this needs to be on a windows PC.