Hi, I re-read your original post and I would like to clarify things.
Firstly, how B&O TVs have AV ports that you associate with the type of equipment attached. For example a SCART to a set top box or a VCR. This is accomplished by using the connections menu. So for example, you use the connections menu on the TV to indicate the DVI AV port is connected to a PC.
Secondly, for non-standard associations you need to add a soft-key (accessed via [LIST], [LIST] as you did) to the Beo4. It may be that your Beo4 does not yet have [PC] defined to its list of soft-keys. To add a new soft-key simultaneously press [LIST] and the stand-by button, the red/orange dot [O]. You should then see "ADD?" on your Beo4's display, press (GO), then press [LIST], [LIST] until you see "PC", then press (GO).
Finally, now you have [PC] defined so that when it is pressed the TV activates the AV port (in this case the DVI) associated with the [PC] command.