SQL Express 2005 on laptop does not connect when Wireless modem is disabled

I have set up SQL Express 2005 on my laptop running WinXP SP3. There is no network or remote connection involved. I am able to connect using SQL Manager Studio or through my application when I am at home in the vicinity of my wireless modem. It does not connect when I am out of range or when I disable the wireless modem. I am using named pipes. The internet connection need not be on, only the wireless modem needs to be on for SQL Express to work. As per a solution suggested in this forum, I added the IP address and my machine name in the hosts file but the problem persists.  When the wireless modem is off, ipconfig shows no ip address. When I switch on the modem, it takes some time for the modem to get ready and ipconfig still shows blank ip address. SQL Server does not connect so long as ip address is blank. The moment the modem is ready a few seconds after truning on, the IP address shows up under ipconfig command and then SQL Server connects. I f ...