Help Java For beginner !?

Hi everyone out there,I need your help.
I just started to learn Java,as a result
i tried to install the JDK so that I can
compile my first "Hello Java" but I'm having difficult
time here.

The Problem is I went to this website( http://www.wikihow.com/Install-the-Java-Software-Development-Kit ) and follow every step and I install the latest JDK from the sun.Abd download Java SE and NetBeans Cobundle (JDK 6u14 and NB 6.7) Final Release.
The thing is when I start to the command mode or MS-dos mode and type the javac there seems it could not find the JDK.

Facts:-
a)in my C hard drive I have I had already the preceding files, which I saw it later
C:\Program Files\Java\jdk1.6.0_14
C:\Program Files\Java\jre1.6.0_07
C:\Program Files\Java\jre1.6.0_04
C:\Program Files\Java\jre1.6.0_05
C:\Program Files\Java\jre6

b)on the same C drive I download the new JDK on
C:\Program Files\Mozilla Firefox
so in this directory I have
jdk-6u14-nb-6_7-windows-ml.exe.

I have list all this because on the above website it says,on the # 13
step,if I mess something my PC would crush or it's not going to be the same.So Please help me what should I do to avoid such problem and get started to learn a new world of Java :-)
Thank you so much