It doesn’t work out of the box with the current version of gmod, but there are ways of fuxing with the L4D assets to get them working. I haven’t tried it, but the kids over at garrysmod.com have been going nuts with it.
Hopefully this stuff makes it into a new version of garrys mod for those of us too lazy to extract files and mess around with configs and such. Gmod has been a big part of the fun over at ubercharged.net for a while now, and we’ll do the same funny stuff here as well once it all gets working.

