Media Center -> Tasks (Settings) -> Media Libraries -> check "recorded TV", NEXT -> Add folders to the library -> on this computer (includes mapped network drives)
Then navigate to the drive location (i.e. mapped drive letter) on the other computer where the "\Recorded TV" folder is for WMC on that machine, and where your OTA recordings from that machine get stored. Check that "\Recorded TV" folder, and NEXT.
I don't share folders between my two machines on the LAN. I simply map drive letters, with "full access" permission so that I can read/write to any drive (and by implication any folder/file on any drive) on either machine from either machine.
And I can also add that \"Recorded TV" folder on the recording Win7 machine to the "recorded TV" library on my second machine. That automatically makes all of the WMC recordings on the Win7 machine appear in the "recorded TV" list (which is actually the "recorded TV" Library) via WMC on my second machine.