all the new trainers can be found at
http://www.xbox-scene.com/tools/tools.php?page=trainers
The ones hosted on gcw will be fine, but the trainer database isn't exactly updated.
Anyways, you have to patch the default.xbe for most trainers. To run them, all you need is a programs called evolutionX and the patched default.xbe file on your HDD. The rest is loaded off the game disk.