Norwegian Mesiro offers a stylish silent small form factor Home Entertainment PC dubbed Merium.

The clean design of the Merium PC combined with changeable covers makes this PC media furniture you do not want to hide.
The Mesiro Merium Home Entertainment PC is powered by a Core 2 Duo processor from Intel running the Windows Vista Home Premium operating system.
Other technical features include 2GB RAM, DVD drive, 250GB HDD and DVI-I, HDMI & VGA via Converter, S-Video outputs.

Measurements of the Merium PC are 10.4x9.2x3.6 inches.

Mesiro sells the Merium PC for 999 Euro (~$1,576) and a cover sells for 55 Euro (~$86). The company ships internationally.
More details on the Mesiro site.