[Graf Paper]

Do a scan for viruses, trojans, and spyware. That's a very likely culprit.
These things can sometimes be made to eat hard drive space.

Run Scandisk to check for errors, then defrag your HD afterwards.

The video stream could be getting cached on your HD and then not getting wiped afterwards. If it's a player that was installed, check that player's folder in 'Program Files' and 'Documents and Settings\<your user name>\Application Data\' to make sure it hasn't kept a copy in one of those places.

If it's a streaming feed through your web browser, check your browser's cache folder to make sure it's not keeping the vids. Sometimes this can be stored in 'Documents and Settings\Default User\Application Data\' or '\All Users\Application Data\' instead of the usual folders in 'c:\Windows'.

Also check 'Documents and Settings\<user name>\Local Settings\' for some of those huge mystery files in the various folders there.

There is a possibility that DOSBox caused an error and the game data got dumped by Dr. Watson, making a huge file.

You need to change your System settings in Windows to limit the size and types of memory dumps and log files. Unless you're very skilled with OS debugging, you can disable memory/stack/core dumps completely.