The SqueezeCenter software will run adequately on just about any PC. FreeNAS also has trivially light hardware requirements. My choice of a hardware platform stems from something that I had conveniently at hand—a box of recycled HP T5700 thin clients (Figure 3) that I had saved from being recycled a few years ago. You can usually find these on e-Bay, or by Googling around a bit.
Figure 3: HP T5700 Thin Client
Thin clients are nice little boxes for embedded projects. The T5700s I have feature a 1 GHz Transmeta CPU, 256 MB RAM, several USB 1.1 ports, Ethernet and VGA video and audio ports. At first glance, they seem more than adequate for hosting SqueezeCenter, given the addition of suitable storage. They are also completely fanless, dead silent, and consume very little power (Figure 4).
Figure 4: HP T 5700 thin client with the side removed
The T5700s come with an internal flash disk-on-module (DOM) on a 44-pin IDE connector. So the obvious choice for a storage strategy was to replace the flash module with a laptop style 2.5" IDE hard drive.
The best deal I could find was a 250 GB, 5400 RPM Western Digital drive for $99. My music library is over 400 GB, but I decided that I could keep a significant portion of the library on offline storage. So I needed only about 200 GB available for music.
While commercial NASes often feature RAID storage, I decided that this wasn't necessary for my purposes. I have all my music backed up onto portable hard drives and the original CDs as well, so I feel that I'm adequately protected. Fault tolerance is simply not a requirement for my dedicated music NAS, so one 2.5" disk was all I needed.
FreeNAS can easily be configured to support RAID 0, 1 or 5 given suitable storage media. But fitting multiple disks into the T5700 chassis might be a challenge. I'm reasonably certain that I could fit three drives into the expansion case, but mounting them sensibly might be tricky, as would be finding a 44-pin IDE cable with connectors for multiple drives.
Figure 5: T5700 expansion chassis (left) vs regular side (right)
The T5700 chassis is small, but it is possible to mount a laptop disk in the standard case. However, I happened to have one of the optional expansion kits on-hand (Figure 5). These are intended to allow the addition of a PCI card, but also provide enough space for a couple of small disks. The metal portion of the expansion kit is perforated to provide extra cooling for the PCI card, or in my case, a hard drive.
The expansion chassis also makes possible a second storage strategy: adding a PCI card with USB 2.0 interfaces connected to external USB drives. They might be 3.5" desktop drives in a USB housing or 2.5" drives in bus-powered USB cases.
Be aware that the T5700 will not boot to a drive attached to a USB port on a PCI card. It will boot to the on-board USB ports, but these are USB 1.1 and not especially fast.