I think you should take a look at [http://developer.valvesoftware.com/wiki/Creating_a_Room]this guide.[/URL] You map must be completely sealed off from the black void. If there are any holes (aka leaks) the map will not work correctly.
gonzales idk what you mean about enclose my map?? i dont think so i ddi that can you show me
and DJive i dont think i made one ill check taht out lol im new
i cant find skybox3d thign djive
I'll be home later and i can upload an example. For now..
go to Textures and put in "tools\toolsskybox"
Create a LARGE square around your map, bigger then the top and bottom of the map.
Select your now large brush and go to tools>Hollow or it might be Edit>hollow
select yes to the 32 brushes. Ta da!
This is not the "correct" way for a skybox, but it will do for now.