@figaro if he cant ping the device, chances are that he cant ssh into it, since we kknnow that you can ping n900. Now there are certain conditions in which you maybe able to ping your PC on the network from N900, but not the otherway round. For example, on my work network, n900 gets assigned the ip 192.168.2.* .. while my PC there has the IP 192.168.1,*. I dont know why this happens, but it does. And i cant ssh in this case to my n900. On the otherhand, my home network assigns ips to everything in the range 192.168.1.*. And everything can ping everything and ssh or whatever is allowed by the devices. The fact that he is unable to ping n900, provided that he has no special software installed on n900 that is blocking the ping, he wont be able to ssh. In this scenerio getting the ping stuff goin is necessary.

Just to confirm, the ping from my home pc to my n900 connected on wifi to the same network is working just fine.