Hi,
I had the same problem, but after some fiddling round I can now play back recorded TV in Windows Media Player.

As you can play from WMP to the recorder, I'm assuming your network is setup OK?

This is what I did (I am on Windows 7, 32-bit, using WMP v12):

Open an explorer window. Click 'Network' and you should see DMR-HW120 under Media Devices on the right. Right-click the icon and select 'Media streaming options'

Select All Networks, from the 'Show devices on' option drop down.

You should see, amongst others, icons for 'Media programs on this PC and remote connections' and 'DMR-HW120'. Make sure that you select 'Allowed' for both these options and press OK.

Open up WMP in normal view.

Under the 'Stream' option, I have 'Allow remote control of my player' and 'Automatically allow devices to play my media' both ticked.

On the left, you should see your libraries, and towards the bottom 'Other Libraries'.

Under this section, you should see 'DMR-HW120', with a + sign next to it.

Expand this and you have options for Music, Videos, Photos and Recorded TV.

Select Videos, NOT Recorded TV and you should be able to see your recorded programs.

Right click on a video and select play. It will connect to the recorder and after 10-15 seconds, should start playing your video.

YOU CAN ONLY PLAY STANDARD RECORDED TV. HD RECORDINGS WILL NOT PLAY.

Hope this helps.

Thanks
Sij