A thread called Unreal 2 XMP, Beta, and Mods on the Atari Forums (thanks Tiscali Games) by Legend's Scott Dalton, outlines some details about what's planned for the upcoming free "XMP" multiplayer add-on for Unreal II. The update describes the three classes from which players can choose, how their skills and abilities mesh, vehicles, scoring and goals, and more. There's also a bit about how map and mod authors interested in participating in the process can do so:

We already have a number of mappers in the beta program who have approached us about making new maps, and we're looking for more people who may be interested.
We'd like to work with mod makers or mappers interested in XMP to answer questions, give tips, or help you get your work off the ground. If you're interested in taking part in modding or mapping, please sign up for the beta program at www.betatests.net and email me personally at sdalton@legendent.com.