KICAD is free and open source engineering design software, including schematic capture and PCB layout tools. There is even a plug-in that does 3D modeling of your PCB. Versions for Windows, Linux, and Mac OSX are available From what I can tell after playing with it a short time, it is complete and well done. I can not see why KICAD would not become the standard tool for open source hardware design efforts.
The main KICAD web site includes a good overview with screen shots. Find the windows installer download from the main site. Then study the tutorial to get started. There is also a site devoted to public part libraries
to get you started.
I found out about KICAD from uCHobby regular “follower” while looking around his “Rancid Bacon” web site. The “Rancid Bacon” web site includes great resources for the microcontroller hobbyist. Pay special attention to the Notes section.