I encoded all my movies on my PC using the ATI All-in-Wonder card using their own AVI formats. I never would encode to AVI again after that huge mistake. After installing the software and drivers to read the files w/ Virtual PC, I couldn't convert them using the various PC iMovie equivalents to another format because they couldn't read these AVI files. I can only play them with Media Player. I never had problems playing my Mac encoded Quicktime files or any Quicktime file on a PC. Also I can convert them to MPEG, AVI, or Media Player files if I wanted.