Need to learn designing mock up with Photoshop

Hi, I need to learn how to use Photoshop to be able to quickly create simple web page mock up. This will allow me to be faster in giving ideas and concepts to my prospects.. I will use screen sharing and voip (GoToMeeting) to receive the course. The language used must be English. Budget: $20 per course. I use Photoshop CS3 extended V10.