One of the basic elements of ERP is having a comon database, with several different front-ends mounted on it.
Having a simple webserver, imo, won't serve your needs, and counteracts with the idea of loose-coupling.
My advice is to use JEE6 on a Glassfish or
JBoss application server.
- Build an EJB Module using JPA and EJB's.
- Build a web module (or web service, or desktop app, or all three) using JSF/Facelets, CDI and a framework like RichFaces or PrimeFaces or .. any other you can find out there.
- Use
maven to provide your EJB module to your front-end.
There you have some names to start with.
If you have no experience with JEE 6, here are 900 pages of fun to start with
http://download.oracle.com/javaee/6/tutorial/doc/gexaf.html
As for AJAX. I know for a fact that richfaces & primefaces have AJAX support, but that's just the ones i worked with.