In JO radiant, click the bsp button up top then one of the options, full for a finished map. JO has a number of changes from quake 3 mostly with entities so any q3 map has to be converted to a JO map.
If you have JO .bsp map file, then zip it in a .pk3 file in the folder "maps" and start up JO mp or sp. Bring up the console and type "/devmapall mapname", that worked for me.
Of course, I have been known to be wrong...from...time to time...