I have been waiting for this feature to finally become available via Soapbox and here it is or here it's not.  I still don't see the Zune Subscribe button on the page as shown in the blog post but it should be around the corner soon.  Additionally, you can always create one-click subscribe links as shown by Cesar at Zune Insider to your favorite RSS video feeds.

The MSN Video folks have updated Soapbox on MSN Video to allow users the ability to subscribe and add someone's video "stream" to Zune. You'll notice a new Zune icon next to the RSS icon on people's profiles on Soapbox for MSN Video.  

When you click the Zune icon, it adds the video feed to the Zune software. For example - when you go to my profile on Soapbox for MSN Video (where I host my videos I post here) and click the Zune icon - my video feed will appear in the Zune software.

Any new videos I publish to Soapbox on MSN Video will then be downloaded into the Zune software which can also be synced to a Zune device. When I post video demos of cool Windows or Windows Live features and announcements - you can put them on your Zune and show your friends.

I expect to be doing more videos in the coming weeks so definitely pay attention here of course and my video feed on Soapbox for MSN Video.

The Windows Experience Blog : Add MSN Video Feeds to Zune as Video Podcasts

[Correction]  There is a link for the Zune subscribe but they are available on the individual users profile pages.  The RSS feeds on the main pages of Soapbox are Shockwave Flash which are currently not converted by the Zune Software.  Hopefully, sometime in the future the Zune Team will enable *.swf conversions of podcasts.