Why not simply play Counterstrike 1.6 ? It can be downloaded for free of the web by now and it's loads of fun. Fairly easy to set up and an excellent team game. We could set up teams like "Creams VS Soaps"

or "mini's VS Meatchoppers" etc.

Just put a password on the game that's posted on the forum and no-one but members get in. Simple as that.