Info here:
http://www.blogjer.com/2009/04/20/ho...-or-blog-post/
There's an IFRAME BB Code in the mods section that can do this but you'll want to limit the iframe bb code usage to just admins and people you trust so you'll also need to install the advanced bb code permissions mod as well.
I'll try to make a custom google docs bb code shortly (a few days) but we have no power here- running on a laptop so can't do much at the moment.