first of all I would recommend you to concentrate on standard compliant portlets (JSR 168), because you can deploy them on both portals you mentioned. For detailed reading tips a skill assessment would be great (e.g. how much do you know about Java web apps ...).
A good starting point for WebSphere Portal Server is the portal zone at developerWorks.
Greetings, Stefan [ January 25, 2006: Message edited by: Stefan Zoerner ]
Author of German LDAP-Book
Committer at Apache Directory Project