I've heard 2009 mentioned, and a quote from a MS Europe representative supports this - "fall 2009". It's already been released outside the US - Canada.
I have a Zune 80, having owned a Zune 30. I got the 30 from B & H Photovideo, and the 80 from Ebay, both cheaper than iPods. I have owned iPods in the past and prefer the Zune, especially for its better interface.
You can access the Marketplace, you just need to be computer literate.
You need to change your region location setting in your Windows control panel to US (this doesn't affect any other settings, including keyboard). This makes the Marketplace appear.
To buy video and music, you need to purchase US Microsoft points. I got mine from here
http://www.microsoftpointsxbox.com/mspoints.php
Note, the one you need is the Xbox Live MS points for a US account.
Update your Zune account with the code you purchase, then choose things to download. You may need a proxy server briefly to trick the Marketplace into letting you download, I use the free Hotspot shield which is automated and easy to use.
I downloaded a few episodes of Heroes using the above techniques