Glen,
Only the USB cable is being used for the BYEOS intervalmeter and all other functions on the 450d exept for mirror lock according to the table on the web link below. The 600d mentioned also will work with only the USB cable including mirror lock. I don't need the mini stereo lead. To clarify, that's my experience, the mirror lock I got from the chart.
For a listing of what features are available on what camera, on the Backyard EOS web site see:
http://www.otelescope.com/index.php?...agrid_bookmark
Also, as a tip, if you save the photos on your PC as well as the camera, you can see all the pics you have taken in BYEOS and review/zoom etc. I think it's a great program.
Cheers,
Damien.