Far as im aware theyre using enhanced versions of the d3 engine, quakewars has some new feature called megatexture. Think it basically lets them use one big texture for ground textures instead of a ton of smaller ones. It also lets them have large maps like bf2 but without the distance fogging effect that bf2 has.
Can grab the trailer of it here;
http://media.pc.ign.com/media/748/748377/vids_1.html
Looks amazing too.
better link here,
http://www.doom3.alliancze.org/trailers ... kewars.zip Posted it a while back.