This is the most beginner question ever, but

Why can't I run an application in Eclipse? I have a JRE installed, but when I go to "run as..." no options come up. I can't debug, I can't run as an application, nothing.

Can someone tell me what's wrong?

edit:

When I try running it from the console using c:/pathname>java puzzle2005

I get :

Exception in thread "main" java.lang.NoClassDefFoundError: puzzle2005

The .java and .class file are in the same directory as java.exe

Here is the code

public class puzzle2005 {
	public static void main (String args){
		System.out.println("You know it");
	}
}

HELP! haha