There is no getting around it, if you want to make levels for RTCW you need to learn GTK Radiant, but I’d argue that you can still use Lightwave for the majority of the detail work for a level:
With the new Radiant & q3map2 you can import ASE format model files into your map file (with texture coordinates and paths preserved). So essentially you can if you like, build your entire level in Lightwave and then import it into Radiant and then compile :). What you will still need to do is create all the collision boxes from brushes and place all the required entities etc. There’s a fair amount of theory behind the way the bsp system works and the way the engine will cull polygons based on player visibility etc which is something you should also familiarise yourself with.
If you are coming from a modelling background you will certainly find the brush (the polygon equivalent) tools in Radiant very primitive, so to me this method seems the best solution to make best use of your skills. You only need to look at new games like unreal 2003 to see that level design is going much more towards environments constructed from models rather than restrictive brushwork.
-Fluffy_gIMp