I usually refer to Artic Silver's thermal paste installation guides. http://www.arcticsilver.com/intel_application_method.html#
Generally, a pea sized dot in the center is good and reliable.
Edit: They have AMD options too.
Hard drive upgraded from 320GB to 500GB.
Specs here: http://panam.acer.com/acerpanam/notebook/2009/acer/aspire/Aspire4810TZ/Aspire4810TZsp2.shtml
It's used. Some general scratches on the cover of the laptop, nothing like a scar or huge...