I think this system is pretty good DIY project. But I wonder if any miniITX system will actually be significantly cheaper than the upcoming HP WHS.
At minimum you need:
Mini-ITX case with power supply: $100
Mini-ITX board: $150
Hot-swap module: $130
Sata controller: $70 (can't find any mini-itx motherboard with 4 sata connectors)
Total: $500, and that is without hard drive yet. If you add 500 GB disk, around $150, that would be $650.
With so many cheaper NAS unites out there, $650 for 500 GB is pretty hard to justify. For example, the new NAS from Western Digital with 1000 GB costs $500. You expand it to 2000 GB by attaching an $400 unit with 1000 GB via USB. Of course, the software running on that unit is limited, while WHS is virtually unlimited (that is if you still have the flexibility to install other apps in it when it ships).
