I can't seem to figure out how to add them in CODradiant

Ok, start from the beginning or just importing them into Radiant?

Beginning.

First, you've made your tree/house/bench/archway/church or WHATEVER. Ok, so you highlight EVERY LAST LITTLE PIECE of your prefab (Shift+Left Click) and you've gotta be careful to highlight all your brushes or you'll be left with an un-finished prefab.

Next: Edit>Save Selection as Prefab and choose a location for it. I use a folder called "Prefabs" which, as you can guess, is easy to remember. o_O

If you want to load them in, go to Edit>Load Prefab and find that same folder you saved it to and load it. But zoom RIGHT OUT on your mapping window if you can't see it immediately. If you don't bother to use it and don't bother looking for it, you'll get a leak because it's not inside your skybox.

Hope that helps.

Great now I can use crappy prefabs from all of you guys :P Thanks²

* drunken reply*

cool

Janova