There is no CAS editor, only a CAS importer/exporter:
http://www.twcenter.net/forums/index...ic=15701&st=12
Look for the post with Cas Import - Exporter by Vercingetorix

You will also need 3Ds Max version 6 or 7 (perhaps 5, but I'm not sure on that). It's an expensive program and I leave it up to you to decide what to do.

A graphics program like Paint Shop Pro (you can download a trial version) or PhotoShop is needed to edit the textures.

Since you are new to this I strongly advise you to search for tutorials on modelling/texturing in 3ds Max and study them well.

Cheers,
Duke John