The language of the post indicated that:
To my surprise, all the stuff I downloaded onto the dns-323 shows up. I was a bit suprised because i didn't have to set anything up
IIRC, UPnP is enabled by default on the 323 from the root folder, everything
would show up.
I turned on my popcorn hour pch-a100 media player
It's compatible with internal HDD, USB, UPnP, SMB, NFS, FTP, WMC, HTTP Servers, and BitTorrent. The only one of those features that would be fully automatic is UPnP in accordance with the 323. SMB or any other feature (except Windows Media Connect) won't publish anything to media-enabled devices, that's what UPnP does; since WMC wasn't mentioned and the 323 was......
...even hypothetically if the a100 did see the SMB share and somehow indexed it, the .mkv files would have shown up and be able to play.
Are these free?
TwonkyVision works for 45 days, then you have to pay $40 for a license and have to install two unsupported packages on the DNS-323; MediaTomb is free, but I had trouble with it properly sharing certain MPEG-4 filetypes.