I will just discuss the differences from the PS2 version, as it is essentially the same...
Graphics are a improved in the following areas:
-the sheen of the helmets is noticable
-New animations for touchdowns, also the shadow and lighting is much cleaner
-some movement of the fans in the stands
-scuffs on helmets, dirt on uniforms
-the mesh uniforms just look better, not sure what it is?
Overall, at first glance, you really aren't going to see much of a difference between PS2 and XBOX...but the subtle additions make the XBOX version slightly better.
Overall, Madden is a great game (but it certainly has its flaws!) I have a hunch that EA Sports is going to focus on all the wrong things in making 2003 and that Fever 2003 or NFL 2K3 will be this years football king...we'll see!