DoomJedi tells me that a new beta is released. it is SplitWolf Beta - version and was created by LinuxWolf and DoomJedi - Team RayCAST. It is the first and the only 2-player splitscreen coop Wolfenstein 3D port - on a cross-platform Wolf4SDL engine. This port brings you the ability to play your favourite Wolfenstein 3D with your friends, on modern computers!ting. Text file included. Available here. Vista/Windows 7-compatible.
There's also a thread for it with a lot more info at Haven Forum.