From what I understand is that UT2003 is built from scratch meaning that it's not based on previous UT engine; however, I wouldn't be suprised if some of the tech from the original was included. As for the UTXBox version coming out, that's based on the same engine as the UT2003 version; however, they are adding technologies and other material not currently present or unfinished in UT2003; such as vehicles, and from what I understand new levels plus what you see in the Unreal2003. From what I read somewhere, they were making slight modifications to several of the levels in UnrealT2003 so that they are easier to manuever around with an Xbox controller. They are also adding levels that will serve the X-box controller really well. Possibly some new weapons as well.
Unreal Warfare I doubt that we may ever see. Now I could be definitely wrong on this, but I do remember that either the Army or the Marines approached the Unreal team and purchased technology known as the Unreal Warfare engine, an engine and combat simulator so lifelike that it was used exclusively by them.