I am thinking about getting a 24/7 NAS/ DVR/ FTP/ Bittorrent/ F@H machine. There are two options for this machine.
1. Re-use my current desktop, which is hopefully going to get replaced with a Mac laptop. This has a low amount of initial energy, as it only needs a pair of TV tuners and a pair of hard drives.
On the other hand, it has a Northwood PIV, and a discreet AGP card. I could swap the 128MB 9600PRO for a PIII machine's 32MB TNT2M64, as the PIII machine is almost never on. I could proably underclock the PIV 2.4C to like 2.0 and undervolt as well.
2. Build a C2D Merom machine, with a PicoPSU, integrated graphics, and other energy-saving components. Of course, the thing has to be manufactured, which could use a lot of energy, but it would be low-power when running.
I think the cost would be similar, but a bit lower for re-using the desktop. If the C2D machine costs $1000+, and the lifecycle is 6 years, it would save $350 of power over its lifetime. The existing machine would need probably $400 of drives and tuner cards for upgrades. Which way?