I shot stuff for someone who wants to review SxS footage on his G5 running 10.4.11. He just emailed saying that it won't install on his machine. Is there a version that will, or does he need to upgrade to Leopard?

Clip Browser 2.6 does support Mac OS 10.4.11, however it only does so on Intel Processors. The G5 PPC cannot be upgraded to Apple's Leopard or Snow Leopard because they only support Intel Processors. I once had a G5 PPC-Quad until I purchased my EX3.

The way I read the requirements, I think you will need at least an Intel core 2 processor:

MAC requirements:
OS: OS X 10.4.10*
CPU: Intel Core 2 Duo 1GHz or higher**

Or of course you could convert it to something that will play on his system...

VLC Power PC version should be able to play the MP4 files directly.
VideoLAN - Official download of VLC media player for Mac OS X (http://www.videolan.org/vlc/download-macosx.html)

BTW Leopard can run on G5 but if you don't already have the disk, they're had to come by and it will have no impact at all on your issue.

Don't know anything about VLC media player - will that play directly from the BPAV folder on his hard disk?

As I said, it will play EX MP4 directly. It doesn't even need the BPAV.
Of course they may want the BPAV for other reasons but for playback of MP4 only, VLC should work. Keep in mind the G5 isn't very zippy compared to Intel Macs. It's simply enough to test though. It requires no codec install.

Thanks - will give it a try

Thanks Craig, VLC worked for my friend.