I have Marketplace working in version 4 that same way it was in version 3.
You may not like it, but here's what you have to do:
- Change your computer region to US, same as you had to do in Version 3
- Create a new Windows Live account with a US address, any address will do
- Create a new US Zune account using the email address from your new US Windows Live account (maybe this part was not necessary, I'm not sure)
It takes a little work, but the hardest part really was coming up with a new Zune Tag
Beware this means that all your Social info such as playcounts etc will be lost, or rather still associated to your old Zune account.
It may not be necessary to perform all this steps, but this is what worked for me.
Also remember this does not allow you to purchase from the Marketplace but at least it works the way it did before and for me it has restored my desire to pickup a Zune HD in the US and suffer with the crippled Marketplace until/if it is eventually release in Canada.
Let me know if you can't get it working and I will try to help.