tedster - 6:11 am on Sep 28, 2006 (gmt 0) Search engines index and rank html documents by url, and not "everything that's showing up in a window". <added>
If the other site in the second frame is being served from their domain, then you are linking to them. The content within the frame is NOT on your site and it cannot be a duplicate issue.
I just re-read your post and I need to revise my first comment. I now understand that the frameset is not generated until someone clicks on the link, so the other site is only showing up as a src attribute in the frame element. So no, that is not exactly a link. However, my comments about duplicate content still pertain -- this is not a threat for a duplicate content problem.
Search engines index and rank html documents by url, and not "everything that's showing up in a window".