I made a box map with hoth sky and snow floor, and I placed a player_start in the middle, but what bsp should i use and the ones I have tried never stop bsping and give me an eror.

How do I bsp the map?

What options have you used, and what error did they bring up?

make sure you didnt make the box using CSG subtract :), make sure its water tight, does that sky shader give out light? if not make sure you palce a light in it also.

best bsp options is the ones with test next to it, then use the final bsp option with bounce 8 for final bsp creation.
A BSP for a box with what you discribe shouldnt take long ( on my pc its well under a minute erm like 10secs :) )

also hows big is the box? i dont think there is a min. for the size of a map but there is certainly a max gridsize to use, make it 1000units by 1000 to start with. hope this helps