IFrame
From Search Engine SEO SEM
Google on iFrame:
Avoid iFrames - or link to their content separately
Content displayed via iFrames may not be indexed and available to appear in Google's search results. Google recommends that you avoid the use of iFrames to display content. If you do include iFrames, make sure to provide additional text-based links to the content they display, so that Googlebot can crawl and index this content.
http://www.google.com/support/webmasters/bin/answer.py?answer=81766&topic=15261
