A while back I produced a nice little animation using Bryce, and thus created an avi. I then converted the avi file to a mpeg so it would be smaller etc etc.

you more than likley know whats coming next, been doing some more work on the animation, added a few things in here and there. so I though, ah grand, I'll take this mpeg back into my editor and cut the new peices in. wrong, it wont let me inport an mpeg, therefore I have to use the avi, to cut to the chase the avi has gone. and I have no idea on how to convert the mpeg back to avi, has anyone got any ideas or know of any software which would do the job?
many thanks in advance.

Depending how small you made your mpeg will depend on the quality you would get back should you rerender to AVI....better of rerendering original work file in Bryce.....if its a long render then leave your computer on all night...thats what computers were meant to do.....Render

(laughs!) Good call, SiRender. And I agree, a little re-rendering in Bryce never hurt anyone. Patience in all things!