PWM motor control

I've seen this matter is a lot talked in the foruns, but I would like to know about something I found on the internet. I need simply to control the speed of a dc motor, and I found this article that tells me how to do it easily using only a chip I already have at home.

http://web.ics.purdue.edu/~fwinkler/616/sn754410_Arduino.pdf

But I have some doubts about it (mainly because I'm a noob). Why there's wiring going to the 9V supply on arduino? And what does the author means when he say on the yellow text box on the Fritzing picture "Make sure the power selector/jumper......."??

I didn't understand where the external power supply goes here!

I would be very glad if you guys could help me! Thanks a lot! =)

Hmm answering you... I will use a Arduino Duemilanove

I thought the pin at the right side of Gnd was a "9V", on that Arduino from the image! So what is that?

And about the power supply, I mean it just for the motor, I will supply my Arduino directly from the USB! Because apparently in this scheme, all the power is being drawn from the Arduino, and I know it's wrong! But I have no idea where in the protoboard I can connect the wiring that comes from the power supply for the motor. Can you understand my question, I don't if I'm being very clear.

Thanks for your quick answer! =)

Well, I understood your explanation. So, instead of using that red wire that goes do the Vin on Arduino, I should connect it to the positive pole of the motor, or in other words, it must be placed in the same column of positive pole wiring of the motor (between those yellow or the green wiring, whatever is the positive one)... Am I right?

But anyway... Doing it, doesn't Arduino still continues to provide all the power to the motor? As you said me to do?

Sorry, if I'm asking much noob question to you! Thanks a lot for the help! =)