What toles do i need to start modding and mapping?
I think it's called Halo Mapping Tools (HMT), and the last I checked, it's in version 3.5. You can get it at the filefront halo site, halo2.filefront.com, and search for HMT.
I would also reccomend several things:
Halo Custom Edition: Lets you use user created content (maps, weapons, vehicles, etc.) as well as having a feature called "developers' mode", which lets you input an exstensive amount of console commands. You can find that here.
If you get CE, you will also need to get this update.
If you want to get into mapping, I would suggest either Gmax, or 3ds Max, which is a bit more complicated (as well as being very expensive, i would suggest just getting the trial)
I would also suggest looking at tutorials at this site:
http://ghost.halomaps.org/tutorials/
And this place has some tutorials for both PC and CE...
Hope this helps!!