The WHEN and WHY of Java technologies

[Jacob]

As a contractor I am trying to get an overview
of the present software technologies so that I
can give qualified advices in these respects.

I look into general topics like "web services",
"client server technologies", "distributed
computing", "application servers", "software
patterns", "security" etc. as well as more
specific ones like "J2EE", ".NET", "XML", "JSP",
"JMS", "RMI", "Tomcat", "JDBC", "Struts",
"Castor", "Soap", "Ant", "EJB", "Swing",
"xDoclet", "HTTP" etc.

I can certainly understand WHAT and HOW of all
these, but I do have a hard time understanding
WHY and WHEN.

What I'd really like to see is a simple "rule of
thumb" listing of technologies and tools; when
to use, when not to use, and what technology/
tool is equivalent/replace what other.

Is there something like this anywhere? Or maybe
a joint effort could put things in place?
(Or is it just me...)

Thanks!