Building the MS-AVR
If you are inexperienced with electronics or engine management, read Lance's megamanual faq http://members.shaw.ca/megasquirt/MS%20FAQ.htm first, it is a great documentation for the motorola megasquirt. The names of resistors are different (naturally), and MS-AVR GenBoard has more features (like the stepper driver and improved controllable flyback), but if you understand one, you will understand the other.
The difference is improved firmware (GenBoard/BuildProcedures/LCDconnect, GenBoard/KeyBoard), and over 10 times more free resources (mainly SRAM is important) for future developments (or your extensions), which you get for the same cost (labor and money) if you choose MS-AVR GenBoard.
The board is just a simple 2 layer board that can be manufactured and assembled at home if you really want, the Surface mount components are easy to work with, generally easier than throughole, except the AtMega128, which is a little harder.
If you are experienced with electronics, and somewhat with engine managament, the schematic and board layout provides enough info to populate a board.
If you are interested in building the firmware, read GenBoard/FirmWare/BuildFirmwareFAQ
feel free to add your notes below
BuildProcedures/SectionOne - Here we solder the processor and the supporting electronics to the board
BuildProcedures/SectionTwo - Here we make the voltage regulator
BuildProcedures/SectionThree - Finishing Assembled GenBoard
to be done: discuss heat sink requirements
GenBoard/BuildProcedures/LCDconnect and GenBoard/LcdFaQ - how to connect LCD
GenBoard/KeyBoard - how to connect ps2 (or AT) keyboard
The old builders' page still contains some useful information:
http://www.x-dsl.hu/genboard/builders/
See ElectronicDesign for generic SW and HW tools.