My friend is using this one:
ASUSTeK Computer Inc.
about 1500 at Sham Shui Po. They are cheap and quite and small. About 3500 HK with 2gb ram and 500gb hdd, plus os cost.
If you want to build one, the Antec Fusion
http://www.antec.com/ec/productDetails.php?ProdID=08738 is a nice choice. Very quite and looks nice, smaller then larger atx ones. About 1200 without power supply also at Sham Shui Po, you can also get them without the display, which give you an extra rom bay. But you have to use a mAtx board, I am using the gigabyte ga-73pvm-s2h they are around 700 HK excellent value
GIGABYTE - Product - Motherboard - Overview - GA-73PVM-S2H (rev. 1.0) optical out, HDMI, quad core, pci express.
Or you can get a mac mini with xhub
http://www.antec.com/ec/productDetails.php?ProdID=08738 The only limitation is the 2.5 inch hard, but you can get a network file server, they are around 1500 plus HDD's, just plug it into your lan.