I came across this nifty bit of code that will work out location from IP address.    In May I talked about adding Meta tags to your website to allow this facility.

See

You can see how it works here -

http://msdn.microsoft.com/en-us/library/aa907670.aspx

Try it for yourself here -

http://maps.live.com/WiFiIPService/locate.ashx

I’m not 100% convinced its using the meta tags described above,  but it seems to be working for me.