Thx for your reply stereosteveo!
Good & bad news. The good one: l I managed to find this workaround just a couple of hours ago:
In my laptop I set the Default gataway setting in the connection properties to the very same as the IP adress of the PS3 (in this case 10.1.1.2). After that, PS3 media server instantly recognized the PS3!!!
The bad one: The PS3 keeps suddenly disconnecting from the media server at intervals between 2 and 10 minutes!!! That sucks way too much because you can hardly see a movie trailer and obviously can't see a music concert or movie....
Also, while connected via the ethernet cable to the PS3, sometimes the laptop gets disconnected from the wireless router and has no internet although it's been stated as "connected" :S
I'm not trying to bridge or share my laptop internet connection to the PS3. Just want to see a movie while downloading some other stuff on my laptop. So that 2 problems are still an issue (PS3 keeps disconnecting from media server after 2-10 minutes and laptop wireless internet connectivity goes down). It may be important to say that these 2 problems don't happen simultaneously (PS3 might get disconnected from media server and still have internet connection in the laptop and viceversa)