I actually was able to get it to work with DNN 5.1.1 and IIS6 - for accessing a page without the extension, not for DNN creating the page addresses, but it should serve our purposes for starters.
You simply need to configure your site in IIS:
1) go to server, open IIS
2) go to websites > Right click on your website lisitng > select "Properties"
3) Select the "Home Directory" tab in the popup
4)Click on the button that says "Configuration"
5)At the bottom of the configuration popup in "Wildcard application mapping", Click on the "Insert" button
6)In this popup Click on Browse> Go to and select C:\Windows\microsoft.net\framework\v2.0.50727\aspnet_isapi.dll
7)Uncheck "verify that file exists"
8)Click ok, click OK, Click Ok to apply changes
9)You can now go to one of your pages to test> IE: mysite.com/forum will bring up a page with "forum" in the Page Name field
Not a perfect solution, but it will work for contact emails, etc.
^_^
Emerson