The Zacate board is a great choice for an HTPC. I'm planning on using a Zacate based board in my next HTPC build with a tiny case from Mini-Box.
I also just built an HTPC with the same nMedia case for a friend last month. Build quality is ok but it looks great in his media cabinet.
Why a 2.5" HD, the 500B can fit a full 3.5" drive, when a quiet full size model like the Seagate 7200.12 500Gb can be had for $39.99?
NCIX.com - Buy Seagate Barracuda 7200.12 500GB 3.5IN SATA 6GB/S With NCQ Internal Hard Drive OEM - Seagate - ST3500413AS - in Canada
I'm also not a real fan of Coolermaster psu's and went with a Seasonic model in my personal HTPC build. Getting a PSU based on price alone is IMHO not recommended even for the lower power needs of an HTPC.
Here are some alternatives from Seasonic & Corsair which are very reasonably priced.
Corsair Builder Series CMPSU-430CXV2 430W ATX Power Supply Active PFC 120MM Fan *3 Year Warranty* - DirectCanada NCIX.com - Buy Seasonic SS-350ET 350W ATX12V 20/24PIN ATX Power Supply Active PFC 80PLUS 120MM Fan OEM - Seasonic Electronics - SS-350ET - in Canada