CS5 can't read Canon G-15 raw files - is there any fix for that?
The ideal workflow, is just as Jim states.
With a new camera, you might need to update to the latest version of ACR (http://forums.adobe.com/community/cameraraw), and be aware that it might only install in the latest version of PS, or LightRoom.
Jim likes PNG (and with good reason), while I normally prefer PSD's (for some other reasons). Either should do just fine in PrPro. I would stay away from JPEG, but then I have a heavy bias against that format.