Sorry - I could have been more expansive in my answer. You asked about the the differences between two model numbers that actually refer to the same camera. There is no A3300 - its an A3300 IS. But in CHDK, its somewhat arbitrary how cameras are identified. The various suffixes like "IS" or "HS" might or might not be used to name the CHDK port depending on the whim of the developer. And Canon changes the name in different parts of the world - the IXUS120 is the European version of the SD940 for example. Exact same camera.
So asking a question here in the forum if you are confused is a smart thing to do.