Sorry for the very beginner question, but what is the difference between a debugger, a decompiler, and a disassembler?

Debugger allows you to examine registers and memory while the application is executing.

Decompiler (or which there are few), takes an executable application, and attempts to convert it into it's source language. Of the languages that are best for this, think of JAVA, and the .NET languages. .NET Reflector is an awesome tool!

Disassembler takes an application file, and turns it into assembly language without trying to reconstitute the original language like the decompiler does. Since regardless of what high level language an app is written in, it ultimately has to be executed in assembly, it's the lowest level, and if you understand what's going on here, you generally have a firm grasp on the application.

Thanks for the great info. That clears it up for me.