Not enough information on 2003 to know. However, ultimately this will depend on the compatibility of existing Java JDKs with Server 2003, rather than specifically JBoss. I would suggest that it would be best to research this as undoubtedly, there will be more information available on the Web regarding this.
About 8 months ago I built a Dell laptop into a Win2003 server with the 1.4.1_02 JRE/SDK and JBoss 3.2.1. It was a PIII 500 w/256 MB RAM which pointed to our Oracle 9i database. It ran quite good, in fact I had trouble convincing the user it was a laptop! (Was used to develop our program templates...not as a production server).