Xbox Gamercard as Avatar

Ok i’m not sure if this can be done or not but what i would like to do is create a field upon sign up that would allow a user when to input there xbox 360 gamertag in their profile. i.e mine is DaveKinetic.

This will the be included in code so that the user on site avatar would display as their xbox gamertag using a .png from http://www.mygamercard.net.

So for example in the profile i enter my gamercard as DaveKinetic. This would then be added to the url http://card.mygamercard.net/GAMERTAGHERE.png making it http://card.mygamercard.net/davekinetic.png and this would then be used as the sites avatar.

If someone were to not include their gamertag it would revert to a blank or site avatar.

Is this something that can be done and if possible can someone help with the coding. Its an idea i want to try but not sure if it will work.