kine wrote:
May be it is a problem how your router works. How the IP of your notebook is set up? Fixed IP? DHCP from router? DHCP from ISP (router request the IP from ISP and bridge it to your notebook...)? May be that when the ISP connection is lost, these settings are lost too, thus all connections are disconnected..

No I think I have eliminated those.
The issue was O2 having problems with line quality that would drop the DSL connection. Among the work they did, they changed modems 3 times, so in total there were 4 completely different modems, (the first 2 the same model, the other 2 different, so at least three completely different types of modem).
In all cases IP is DHCP from the router, and IPs were still working, and computers on the LAN could continue communicating.
It originally happened on my Vista laptop (dell), now on my XP (HP), the Dell I tried on Wifi and hard wired, the only common factor appears to be Navision and SQL 2008.
And remember I am talking about SQL and Navision on the same machine. NOT a separate server.
If I pull the modem out of the wall or turn off WiFi, it has NO effect on Navision.
It really doesn't matter, its just a local machine, but its very weird.