For "virtual machine name" do you want the implementation name or the specification name?

The implementation name, although we don't really care (it's just something we want you too look up in the documentation - the grade on the assignment doesn't depend on what the value of this property is).

I cannot find java compiler "javac" in my installation of Java. What is the problem?

You are required to install Java 2 SDK (Software Development Kit), you may have installed JRE (Java Runtime Environment) only. JRE is required for running java applications so that would be enough for people who don't want to compile code but for this course you need Java SDK. JRE is included in SDK package so you don't need to install it separately.