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?