tedster - 3:43 pm on Jul 6, 2010 (gmt 0)
If the fragment that is isolated its own URL (#2) is not a good landing page for search users, I would probably use a noindex robots meta tag. A canonical link to a much more extensive page is like to be ignored, because the two are not close enough.
I have no idea how best to handle 3)
Iframe content is not currently considered part of the parent URL - so you have no worries there. Each URL gets ranked based on the content in its own source code.