The meta tag needs to be included in the head section of the page.
This blog post shows one way to do it:
http://www.dotnetnuke.com/Resources...er-10.aspx The change should be included in every skin file that you will use.
If you want to do this for every page in every portal of your install, you can directly edit Default.aspx in the root of the website directory to add the meta tag. If you do it this way, remember that it will be overwritten if/when you do a DotNetNuke upgrade.