I asked this question myself awhile ago. The 03 swingarm looks way better! but you shouldn't because it's a different length and it'll mess with your handling. As for actually fitting it,....I don't know.
to really know, you'd have to measure the width of the pivot point to see if it would fit and also make sure the hole the shaft goes thru are the same sizes. If you have access to both model years, measure them to see if it is even feasible first. I doubt it since the 03+ were completely redesigned from the ground up using a different rocess to make the frame and swingarm (control filled) so I bet the dimensions are off just enough to make it not work. But I could be wrong and I often am!