Thats good advice except usually OEM factory units like gateway
usually dont use a common form factor like atx or matx for their cases
plus their power supplies are usually lacking connectors
for example with Dell and Hp you need parts like these for using different power supplies
http://www.directron.com/hp24mini.html?gsear=1%20adapters
that is just to show their can be proprietary differences with some of their
gear
they have gotten better about it
in the last ten years most of dell,hp gateway parts are all common pieces
even dell which used to use a BTX style case has in past few years started to
use atx form factor for PSUs and some cases