Gateway used to use AMD processors, but they have since switched to using only Intel processors. One of our machines is an Gateway SB 1000 with an Athlon 1000 and it has a regular heatsink and fan on it. No fancy ducting. It is quiet too. Not sure if they will go back to AMD or not.I would wonder whether they can keep using those ducted heatsink systems if and when they move to AMD's processors..
As for the Dells being quiet, they are very quiet. Sometimes I have trouble telling if they are on. I will agree that the servers are loud, but that shouldn't be an issue. Cooling is the top priority in a server, not noise. In my opinion Dell makes great computers and servers for low prices.