Hi:
The advice I am about to give you is based upon a simillar situation I had when I was building my home network. I cannot remember the exact procedure or where exactly the options are on Windows to sort this out (I assume you are using Windows). Hopefully someone will be along at some point to fill in the blanks or correct me accordingly.
Right:
Forgetting that the Beomedia is an A/V device, as it is connected to your network it is in effect another PC. I have not used a Beomedia but I assume you have it wired by ethernet to your router as opposed to wireless (I am unsure if the Beomedia supports wireless in any case).
I also imagine that you are refering to a wireless router as opposed to a wired hub?
The principle is still the same so I shall proceed:
The main PC that is attached to your router (or the one that was attached when you setup your router) needs to be reattached by ethernet). Then, in My Network Places or whatever the equivalent is in Vista (you need to fiddle around in the general area) looking for an option that is vaguely simillar to "assign a ne IP address to each device that joins the network". What should then happen is that a new IP address is given to the Beomedia which does not conflict with the IP address of the other items on your network and thus you should not recieve that warning message any longer.
At present the reason you are having this issue is because one of the computers on your network has been assigned the same IP as the Beomedia and this is causing the problem.
I hope this helps, sorry if I am being too vague - I cannot remember exactly how I sorted this out, but what I have said should point you in the general direction.
Graham