From what I gather you can use manual strobe with Av/Tv but I could be wrong. You do have to have the magnet installed to use when the camera doesn't produce a pre-flash like with the G series in manual mode.
Fuck I love the S2000 though, I'm so damn glad they made it.
I called Reef Photo and asked about the magnet and was told to just leave the magnet in all the time. Some of the Canons (like the G series and S90) don't function TTL in manual mode and therefore you need to have the strobe set to manual as well. By leaving the magnet in, the FO cable will trigger the strobe to fire when the camera's flash fires off... best to keep the camera's flash set at minimum.
When shooting auto, P. Tv or Av, having the magnet in will not interfere and you can have the strobe set to STTL if you want it to synch with the preflash. Again, if you want to control the strobe manually with those camera modes all you need to do is set it to manual or use the STTL overrides. :-))
Will see how all this works out next week.... of course, that is if I can also figure out lightroom 2 (my first time trying it out will be this trip).
Unfortunately I was not able to install CS3 on my new netbook as I lost the serial number for it. Even tried to install am old photoshop from many years ago as I had installed it on several notebooks already... for some reason this time it asked for a serial number as well. :-(
Leaving for Dominica Sunday and will be taking my first giant stride Tuesday!!