Hello!
Thank you for Nabble, first of all.
Im having the same problem; upon pasting the embeding code in the HTML editor, all I get is the link to my forum at Nabble. Im working in GoogleSites, and I've seen Nabble embeded forums on other sites powered by Google, so I dont think the problem here lies in the site providing company.
Here is the link, I hope you can help me fix this problem
http://sites.google.com/site/kt3ska/forump.s. Does it take time for it to embed or should it happen instantly, right after save the page with the code in the HTML?
Thank you.