it looks like there is a typo in the URL (Final vs FINAL), you should be able to use http://downloads.jboss.org/portletbridge/2.3.0.Final/JBossPortletBridge-2.3.0.Final.zip until this is fixed.
Hope this helps,
Filename OK, path not - 2.3.0.FINAL
The requested URL /portletbridge/2.3.0.FINAL/JBossPortletBridge-2.3.0.Final.zip was not found on this server.
Apache Server at downloads.jboss.org Port 80
Sorry about that!
Small copy/paste error on my part, and then I was moving and did not have a chance to fix it until now.