Yes. Seam 2.1 will probably only support JBoss 5 CR2 and above.
How would you place
supportin the scale between
running it on 4.2.x will result in a burning pile of debrisand
let's push some traffic to this new 5.x version we just got out? ;-)
The support for Seam on both JBoss 4.2 and 5 should be equivalent, but 4.2 is a more mature and more tested platfom.