Yes, xbox-scene is the place to go.  I found that the ltools mod (via a mech assualt save game exploit) works very well.  It does everything for you, and allows you to uninstall itself and return to a normal xbox.  
  There is also "Softmod.Installer.Deluxe.v2.0.Xbox-Hq" which is what I actually used to completely mod things.  It's a bit more complex in that you have to tell it each step of the way, but I liked having a bit more control of things.
  Oh, and the platinum hits version of mechassault doesn't work, you need the original.  All that's explained on xbox-scene though.
  Thanks for the link.  Good luck modding your xbox.  =)
  Anyone else actually use an xbox in their cab?