The JDK (Java Development Kit) contains development tools, including the
bytecode compiler.  The JRE (Java Runtime Environment) contains just the
runtime.  JDK became the Java 2 SDK in v1.2, but has (apparently) again
become JDK.

SDK vs. JDK is just a naming convention; no difference.  5.0 is I
believe really 1.5.  1.5 adds some interesting new language features, but
it really depends on what you can expect your users to have installed.
You won't be at any real disadvantage if you use 1.4 right now, and
your users will be more likely to have 1.4 than 1.5.

No idea.

Beginner's questions are best handled in comp.lang.java.help

Sun employs a bunch of bored people who have nothing better to do than
to rename and renumber products. These people have a fixation on
renaming and renumbering Java - after doing the same with other Sun
products like the Solaris OS and the C/C++ compiler for years.

E.g. once the Java SDK (Software Development Kit) was called JDK (Java
Development Kit). Than some of this bored guys at Sun renamed the JDK to
something like "Java 2 SDK". Later, still bored, they once again renamed
it back to JDK (with Java 1.5/5.0).

The same happens with the numbering. Suddenly Java 1.2 was called "Java
2". But of course Java 1.3 was called "Java 2 SE 1.3" (or something
along the line). With Java 1.5 they did it again. Java 1.5 is suddenly
called Java 5.0.

Enough? Well, still not for the bored guys at Sun. How would one now
expect the next major version of Java to be called? "Java 6.0", right?
Wrong! That one will be "Java 6". Sun will drop the minor number. Of
course, this will open up a new can of worms, because how are they now
going to identify maintenance releases? I would expect atrocities like
"Java 6 SE Build 1.6.3_b24" in the future.

I would suggest you start with Java 1.5, alias Java 5.0. Unless you have
a good reason to start with the older 1.4 JDK/SDK. Such a good reason
might e.g. be that your textbook (you do have a textbook, don't you?)
doesn't cover the new Java 1.5 features (e.g. generics).

If you follow a 1.4 textbook but you use Java 1.5. you will get a bunch
of warnings from the compiler because one is supposed to do some things
differently in 1.5.

NetBeans is Sun's free IDE, which is a classic IDE (supports the usual
things on expects from an IDE).

Java Studio Creator is a commercial Sun product, which is centered
around visual "programming". One is supposed to drag and drop stuff to
somehow assemble an applications. Some years ago one would have called
that a RAID tool.

JSC is unsuitable if you want to learn the programming language.

Use non of these. Consider using the command line tools that come with
the JDK/SDK, so you get an idea of how things really work.

If you are more interested in object-oriented programming than Java,
consider the BlueJ IDE http://www.bluej.org That IDE is particularly
made for students.

/Thomas