That's because when you create that cube, you're only creating one brush, so when you're inside it, you can't see the outside faces because you're not supposed to be able to.
Why don't you try running through
these mapping tutorials and see if that helps. They were created for jk2 but just about everything applies to jka and you should be able to figure out any inconsistencies, if not, just ask again.
http://www.richdiesal.map-craft.com/...als/index.html