One of my Media Centers at home is an HP z555 and I recently was forwarded this article by David Powell, Making the switch: Tivo to Media Center and he’s got lots of tips for optimizing things such as the video card, Extender and the z555’s airflow:

One last thing on cooling: a friend reversed the two fans (CPU fan and the side fan) inside the z555 and it now runs much, much cooler.

Since my z555 is in a fairly open space I don’t have heat problems, but I imagine many of you might if your z555 is in a cabinet, so if you’re the intrepid type you might want to try reversing your fans.