I'm interested in compatibility of parts of the 2003 (euro-only, I know) A3 with the B5 A4/S4. I know the older A3's were similar body style to the B5, but I didn't know if there was a significant update by 2003 (more towards the B6 and current B7 A4/S4 --- I think its a D9? something like that).

Appreciate your help in advance.

-r

Allthough it was facelifted in 2005, there were no major changes. That model is allmost identical with the current US A3.
Picture 8P 2003:
<img src="http://www.activauto.fr/photo/site_audi_a3_av.jpg">
If you mean the generation before that one, it is the 8L, which was produced between 1996 and 2003, with a facelift in 2000.
That car shares a lot of parts with the 3rd generation VW Golf.
Picture 8L 2000
<img src="http://www.autoweek.nl/images/800/c/90940ef79c0df3f44f9bd411faf249bc.jpg">
<img src="http://www.autoweek.nl/images/800/e/0e02774d4b2cb2d47cb674da080f32ae.jpg">
<img src="http://www.autoweek.nl/images/800/d/5750fc2cac58520e47aedab1d24e739d.jpg">
<img src="http://www.autoweek.nl/images/800/7/6dee4e452deeb004258f2f175321d3a7.jpg">
I hope this helps..

Cheers,

Dirk-Jan