Have you recently updated and ran your anti-spyware and anti-virus software?

Have you tried using other browsers ? firefox or netscape.
It might also be an idea, to sign up on a technical forum and ask on there. I wish i could help you more.

regards
CP.

Are you sorted yet ?
 

Have you solved your problem yet ? If not here are a few things to try. I had the exact same problem once after installing the quicktime plugin, I thought it would just allow me to view .mov files - but instead it changed the way my pc handles many video files. The installer does much stuff you don't want or know about (in the background) including adding itself to the startup group. I ended up uninstalling it. It also makes downloading MPEG or MPG files almost impossible and wants to play them inside your browser instead. If you have not installed this plugin or similar, then try using Firefox. Go to "options" and then the "content" tab. There are settings in here to manage how the browser handles various file types - including MPEG and MPG files, for instance it will let you play them everytime or save them to disk everytime etc. etc..... I hope this helped you, or anybody else.

No, haven't solved the problem yet, but you're the second person who's suggested QuickTime might be responsible. I'll check out the settings on Firefox as you suggested. Thank you!