HN Hardware Hackers: Fundamentals of PCB Design
There have been a number of discussions on HN about doing circuit boards and wanting to learn how. Here's a good intro by an recognized expert in high-speed PCB design:
http://www.techonline.com/electrical-engineers/education-training/courses/4000356/Fundamentals-of-PCB-Design
For the mechanics of actually designing the electronics and laying out a PCB I'd recommend the free training videos from Altium:
http://altiumvideos.live.altium.com/
intro:
http://wiki.altium.com/display/ADOH/Tutorial+-+Getting+Started+with+PCB+Design
Keep in mind that this is professional-grade software (not free).
A good KiCAD (FOSS) tutorial can be found here:
http://www.youtube.com/watch?v=okAUlHsTcg0
http://www.kicad-pcb.org/display/KICAD/KiCad+EDA+Software+Suite