Extract the zip file while in the /Activision/Cod 4/usermaps/ folder. 

So the path to the map files is
/Activision/Cod 4/usermaps/mp_testjump/

Start up Call of Duty 4. Click Mods. Launch ModWarfare. Start New Server. Start on any map in Team Deathmatch or Free for All. Once loaded up. Open console and type /map mp_testjump

Enjoy.

From Croc