I have some interesting findings, now that I am using a 700, an N800 and a desktop PC with wireless connection on the same wireless router. When the Desktop is connected then both Nokias can connect with only link-local IP. If I put the Desktop to sleep then the Nokias connect normally. If I wake the Desktop once the Nokias are connected then it connects fine. The Desktop uses a D-Link DWL-510 PCI wireless card.

It seems that the Desktop has some priority over the Nokias... Reading back this thread some of the situations might be explained by this.

I don't know enough about wireless networks, if anyone can help then please do so.