I wonder if it is bad for SEO to use frames? For a certain reason I have to do this on one of my sites. I don't want a part of text area of the website to by crawled by the spiders, so I will insert a frame and will block the page in the frame using robots.txt file (I cannot use an image, as this content is dynamic).
It's not the way to prevent search engine from crawling it. Using robots.txt and the right meta tag will do it.
Your answer lies in Google help, your method of idea has a sound theory, depending if it will work or not is a whole new issue, your best bet will be to test the theory and see if it works. http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=34445
Framing is the black hat seo techniques and according to Google rules,Google does not support framing.so avoid framing its not good.