Fast User Switching

I'm considering switching to the AppleTV 2, and have 2 questions...

1. Since it only streams, I need iTunes running all the time to access my content which means someone needs to be logged-in. If a different person wants to login while the AppleTV 2 is being used, can they use 'fast user switching' without interupting the streaming? Will iTunes still stream to the AppleTV 2 even if its account is in the 'background'?

2. The specs for the AppleTV 2 say it requires iTunes 10.1, which in turn requires Mac OS 10.5. Is this a "firm" requirement, or will it still stream from an older iTunes under Mac OS 10.4?

Thanks