[Rob Barron]

If you are doing this purely for photograh purposes then there really is no difficulty at all. Simply use as plain a background as possible that is of a contrasting colour to anything else in the photo. That makes it easy to select and then to delete. Put the BG image onto a lyer below this layer and there you go, couldn't be easier.

If you are wanting to do it for video purposes then the best way is to use video software like Premiere Pro. Having said that, Photoshop CS3 does now have a lot of useful video tools that can be used for all manner of video purposes like titling, timelines and so forth.

I think from reading your post that you are only talking about for photography which basically means you don't need true chroma keying at all. You simply need a plain background, nothing more really.

Cheers,
Rob