Hi-res Achievement and Trophy Images
Solution 1:
When I wrote a way to pull achievements onto my web page there wasn't an official Xbox Live API (though this may have changed recently). Instead I found an API that someone had hacked together:
http://duncanmackenzie.net/blog/put-up-a-rest-api-for-xbox-gamertag-data
http://drupal.org/project/xbox_api
It's not currently maintained, and if I remember properly you can't get very large images, but to the best of my knowledge it is the only way to pull data directly from Xbox Live.