You don't even need the original game to run it, just download and start playing! Duke finds himself transported to a strange fantasy realm where humans are under attack by monsters. Using new weapons and some strange spell-like abilities, Duke decides to help the humans out so he can get back to his own world. Siege Breaker features big environments filled with secrets and a slight medieval/fantasy theme. It's not your usual first person shooting game, for sure, but the level design is good and requires a lot of poking around, just like those lovely old school games of yore. Give Siege Breaker a shot and soak in the retro goodness for all it's worth!
In version 1.1, a new level, Castle Demonhorn, and a new playable character, Jedrik Demonhorn, were added.
The current version, 1.2, has 8 new levels, 10 new abilities and lots of refinements. A huge update!

http://two.wgrealms.com/
http://fissile.duke4.net/fissile_wgr2.html
http://www.moddb.com/games/wgrealms-2