This may be a dumb question, but here goes.
Looking at the Borla web site they list no exhaust for the '03 Xterra.
They do list part #14873 cat back exhaust for the '00-'02 Xterra.

Is there some difference big or small which might make this not fit the '03-'04 models?
I know the Gibson cat back states for '00-'03 models.

I would like to know before I go spending hundreds of dollars only to figure out it won't fit due to some silly bracket or something.

Ok, I just got off the phone with Borla and it will fit an '03 no problem.

-***- HEADS UP -***-

If you want this exhaust now is the time to act!!
Borla is discontinuing the cat back Xterra exhaust!
They have 4 left in stock and are selling them off at $333.44
You can't come close to that price at any distributor I have looked at - only direct from Borla.

The fitment issue pertains to the fact that the Borla has a flange connection to the factory pipes. At some point (I believe mid-2002 on) Nissan changed this connection to a slip joint and thus, the Borla is not a direct bolt-up for these later models. Should be easy enough for a shop to modify though.