Specifications, manuals and manufacturer support often are not helpful. Therefore you should retrieve information from other sources too:
Highly recommended is the survey by Kenneth E. Harker http://www.linux-laptop.net/ .
open hardware - The Open Hardware Certification Program The Open Hardware Certification Program
HARDWARE.doa.org - dedicated to the hardware aspects of (Linux) computing http://hardware.doa.org/
How to Build a PC FAQ - excellent hardware overview by Billy Newsom
Last but not least the WWW itself.