Hi,
It has been a while since I enabled the media server on the 320, but it is pretty simple as I recall. Log on to your 320 web GUI. Then go to application management and go down to UPNP, as this is the media server. This is all assuming you have the media on the 320 of course. There are a few problems and issues however, because the 320's firmware unless you install the latest 2.02 beta does not support the correct alphanumeric folder/ file structure, i.e., you will end up with a random bunch of folders with random files within. If you enable the UPNP function, you will get to select which folders you want to share, and I believe no user settings are available / necessary. You would access the other restricted folders via your network shares and you can select whatever user settings you would like there. If the folders you do not want to share are not subfolders of the ones you do, you are OK. The 320 does not transcode anything so if the files you want to play are not supported by SONY, you will either have to convert to a supported one or no play, and SONY is known to be picky.
The one known downside about the beta firmware is that it is not down gradable and I would not count on it or any future firmware to be down gradable. They don't tell you this, and unless you would research it on the forums, but on the other hand, I think the latest 2.02 firmware is better than the stock 2.00. Not sure if I covered what you wanted. Good luck.
PS. You could just try enabling the media server in the stock firmware to test if the various file types are supported by the SONY devices, if they are then it should be no problem with the beta firmware. Other options, convert media, go the install TWONKY / fun_plug route.