Hi Stuart - "a light just went on here" - the "magic" of WiFi (and it is a magic, not a science!) is that if anything is wrong with your security settings, it does not always come up with the error message you expect. A connection but no IP address IS one possible condition that occurs.

Given that you have tried different WiFi adapters and tried connecting to different WiFi routers, I am starting to think this may be a security setting problem.

A lot of the older cards can only support 802.11b (not G or N) and a lot will not support WPA or WPA2 encryption only WEP.

On your WiFi router, have you tried turning off all security and make sure that it is set to support all speeds of WiFi - i.e. 802.11b and 802.11G at least?

I would not leave the router like this as it's an "open door" for those in range to use your network, but to test you could do this. Ideally at the end of the day you need to be running 802.11G or N and WPA2 security, but if the hardware you have wont support this, then you will need to set it to the best you can get but initially lets see if you can get things working totally without security enabled.