The forums are awesome (round of applause for Gren!!!) but... wtf does this thread have to do with.... oh. well... it does have to do with mapping... umm...... do you mean a SP > MP map conversion? just get HMT3.5 and read the tut.... if thats not what u meant, please clerify.
Edit: Wait a sec... when you said upload, did u mean u have a .map file that u would like to play with halo CE? just put it the maps folder. or, did u mean u have a .obj, or whatever type of MAX file thingy, file and u would like to make it a .map file? Read the tut that comes with HEK... sry, but i cant really help u there.