Tim, I think you need a plug-in (free) to open RAW in CS3 (not sure, my DVD drive hasn't arrived yet so my copy of CS3 sits tantalising me on my desk . . . .). I'm pretty sure that's what I read on the forums.
Yes ... you can download Adobe raw and put it in the right plug-in folder and it will read the RAW from the 1D Mk III ... apparently the raw editing is really good with CS3