So, multiplayer is finally coming to Unreal II, but just what is this 'XMP' that everyone's talking about. Well, to give you all a better idea of what we can expect from the upcoming Unreal II Mutliplayer Add-on, here's a quote from a snapshot of the old Unreal2.com site, taken before multiplayer was originally pulled from Unreal II.
In the new expanded multiplayer game, player teams will fight for control of planet surfaces and alien artifacts using nanotechnology replicators to build ever more sophisticated weapons such as automated gun turrets, force fields, sensors, recon and repair robots, and more. Players will choose one of three player classes at the beginning of play - class selection establishes a balance of speed, special abilities, armor, and firepower. All races, abilities, weapons, equipment, and tactics will have precedents in the single player game - but the expanded multiplayer experience brings everything together at the same time.
Remember, we still don't know whether or not all of these features will make it into XMP. The quote above just tells us what was originally planned for multiplayer gametype.
No news on when the XMP add-on will be appearing yet, although with UT2004 due out this fall, it's likely that Legend will try to get XMP out sometime this summer.