Well guys I got custom resolutions working 100% and the FPS unlocker works as well so you can also play the game at 120+FPS if you really want to.
Ok now on to how to actually get this to work.
First Download the
DarkSoulsFix and put it into your Halo 2 folder
Then click on DSFix in the folder, here you will see a lot of options but there are only 4 you really need to worry about.
-Set your internal rendering resolution higher if you wish but if not keep it the same as your normal desktop resolution
-Set your Display Width/Height to your normal Desktop resolution
-Under Window & Mouse Cursor Options enable Borderless Fullscreen
-Then at the very end Force Windowed mode
Feel free to mess around with any of the other settings and again if you want you can unlock the FPS in the game as well.
[MAKE SURE TO HAVE WINDOWED MODE ENABLED]