Streaming video AVI playback

If I have posted this in the wrong forum sorry, but not sure where to go. I have sent a couple of emails to support group still waiting on reply, so I thought I would try here.

When I go to the internet on tv2 can see the streaming sites ( e.g I want to watch this.com) but when I click on a video says cannot play AVI.

Second issue is that when I download a movie; convert it to mp4, can see it on the itunes but when I click on it to play all I get is the spinning wheel…15 minutes in and its still spinning!!!

I have a Mac OS X with version 10.6 8 with Snow leopard, and updated itunes to see if that would resolve the issues…nada.

Any help from the community would be appreciated.

P