Mark another option might be DSLRRemote.
http://www.breezesys.com/DSLRRemotePro/index.htm
At a guess there will be plenty of other options around for controlling a Canon DSLR from software but for my Powershot they seem to be the only player. I've been using the avaluation version a bit and so far so good. I'm also playing with CHDK which lets me write code and put it on the SD card to automate tasks as well as accessing capabilities which Canon built into the camera but not into the user interface.
I'm not sure if it's available for DSLR's but there is work happening on getting it going on the 400D (one post at
http://chdk.setepontos.com/index.php....html#msg34785) looks like it might be. There are more discussion thread's at
http://chdk.setepontos.com/index.php/board,33.0.html
The version of CHDK for my A640 powershot is amazing in what it unlocks and the things I can set up, worth a look and probably free if it's available.
Bob