I'm a huge fan of home media servers, but the enduring problem with them is that the available network media streaming appliances have, by and large, sucked. The Xbox 360 recently received a firmware update that improved its capabilities, but a hacked Xbox running Xbox Media Center (XBMC) is still probably the best product available for the job.
CNET, however, has recently published a review of the Linksys DMA2200 that might have me changing my mind on that. It supports all the codecs that people are actually interested in using (Divx, Xvid, Windows Media, H.264 and MPEG1, 2 and 4), which is not something that can be said of, say, the Apple TV. It can stream and control live TV from a PC, effectively turning your PC into a remote PVR. It also supports 802.11n networking, which is enough to do HD over wireless.
Anyway, if you're interested in knowing more, just follow the link. [CNET]