Wow, this was a little unusual.

Wireless laptop running Vista SP1 connecting to a Micronet wireless router, using simple security i.e. WEP without mac address filtering, connected in turn to a cable modem suddenly the laptop stopped being able to connect to the wireless network. (Event viewer showed the laptop did not receive a response from the router when it tried to connect.)

Everything else on the wired or wireless side was still ok (about 3 XP machines, Wii, Xbox and a few Windows Mobile devices) and the laptop would

happily connect to everything else tried Unsecured, WEP, WPA etc.

Eventually we ended up using 'arp /a' and 'ipconfig /all' to find that the Micronet wireless side was now, for reasons we will probably never find out, using the same mac address as the laptop.

A hard reset of the router and resetting it up was done and again everything working (there wasn't a simple way to change the wireless mac address on the router only the WAN's mac address could be configured - and the laptop was using an inbuilt Raylink card which also was missing this option).