Okay everyone, to clear things up - the PAL Wii will output at 480p with a component cable hookup and the progressive scan setting chosen in the Wii system settings.
If you are not using component cables and just using the supplied composite cables, the Wii will output at 576i (576 lines interlaced)
This is exactly the same as the Gamecube:
Component cable plugged in: 480i,60hz (non-progressive scan games)
480p,60hz (progressive scan games)
Composite cable plugged in: 576i,50hz (standard setting)
480i,60hz (games that support 60hz mode - there were a few on the Gamecube)