Here’s a great wiki site showing you good information on how to hack the ASUS Eee PC including how to add a GPS unit without breaking your arm off.
There are several points on the motherboard where power can be draw, for devices requiring 3.3v or 5v. Ground is universal and allows for short wire runs. A diagram over the points can be found on the research page.
The signal wires thickness is 30 AWG and 24 AWG for the power and ground wires. The wire type is called wire wrap and used for prototyping and repair work. Mine is Tefzel insulated and made by Habia Cable. Some of the devices are held in place by double-sided 1 mm thick foam tape. To cover up and prevent shorts I used 3M Kapton 10 mm wide tape.