My good friends over at somethingawful.com have whipped up a guide to making your own FPS mod. I know a lot of you out there are dying to make the next Counter-Strike clone, so here's one of the guide's tips:
Always keen.For a Counterstrike based mod, just add on the name of the game you intend to port Counterstrike to (e.g. Counterstrike UT, Counterstrike Q3a, Counterstrike DH3) or if you don't have permission to use the Counterstrike name, use something to do with terrorism or policing or some hideously long and obscure random set of letters chained together, e.g "U.N.M.A.T.S.A.D.L.P.C" ("Uzi 9mm Anti-Terrorism Strategic Annihilation of Dolph Lundgren's Presidential Campaign"). Try to reference the fact that the world is in danger and only the player's elite team of lagged snipers can save a plane from being hijacked or the President's daughter from being kidnapped or whatever the hell your "realistic" goals are.