I'll tell you now, 'fuck' the external fans, just keep it in an open-aired type place, if you can. I've had 4 different Xbox 360's since they came out, including a first run and they all ran perfectly. I decided a couple of weeks ago to get the dual external fan that attaches on the back of the 360, and within about 4 hours of playing it (not 4 hours in a row), it started flashing the red and stopped working. So, I took it off and haven't had one problem since. I've heard many, many mixed reviews about the external fan, I think the idea is good - it just seems to have some power issues transferring the power from the power cord through the external fan to the 360.
My $.02 of course.