Here is a TuT on how to mod your Gears 2 Rank To Level 100!

Step 1.) You are going to need a Profile that is level 100, there are quite a few people that give them out.

Step 2.) Unplug your ethernet cable (or Wireless adapter) from the back of your Xbox 360.

Step 3.) Sign into the level 100 profile, put gears 2 in.

Step 4.) Go into the training grounds, and press (A) on the first one.

Step 5.) As soon as you press (A) you need to sign out of the level 100, and then sign into the profile that you want to be level 100 (IE. your main)

If done correctly some achievments should start popping up, and when you go into multiplayer it says you have the star, now go play 1-Round of horde and it will say you are level 100, with a TON of Xp

(Im not sure if this is in the right Section )
Hope I Helped
FocuzZ