I am currently doing this on my XBox 360s and also to my PS3s. I am using a D-Link DNS-321 to store and stream movies to my systems. via LAN it works very well, via Wireless I experience some lag issues. ONe of my 360s has an 802.11n card and works just fine.
So you shouldnt have any problems streaming from a network hard drive or a PC with Windows Media Player, TVersity or other streaming software.
But compared to the original XBox's with XBMC, you will find that XBMC is more compatible and forgiving for media formats than the X360.