From what I read using the tool 'arsenic' is what seems to be the best way to convert the maps. However, I can not for the life of me get it to run. I even installed slimDX. Also, the forum on halomaps.com is always 'in maintenance' so theres no help from there.
I uploaded a link containing LOADS of (xbox) halo 1/2 map editing tools including arsenic since stuff like that is rare to find on the internet o.o .
Anyways I got this mod pack from a piracy site from a user named notaru. So, I don't know if it has any viruses or what-not but my computer didn't detect anything.
Halo_Mod_Pack:
http://www.mediafire.com/?1d4smhzb7li2bxqif anyone wants to links to tutorials for modding the xbox version of halo, plz post them

P.S. I've been looking for a halo 1 soccer map. Warthog is the ball, pistols shot rockets, shot guns shoot multiple rockets, and its a giant box in the middle of the blood glutch map, and if anyone has it plzzzz upload it. Many thanks