I was afraid of your answer, I'll need to be patient...

Here what's appening:
When configuring an EJB3 project, libraries must be bound to the right server, so I create a new one :
Define New server -> Installed runtimes ->Add
Select Jboss 4.0 Server Adapter Runtime, give name, path,... validate
The new jboss5 server configuration is created OK.

But when choosing this new server to bind the libraries, I get the following error:
The selected configuration("jboss5") does not contains the expected EJB3 libraries, please install JBoss with EJB3 enabled...

This append also when selecting "all' as server type.

Project compilation can however be achieved using user defined libs.

The created server can be managed with the server view.

Hope this helps...