The question was about Selenium RC, miki, you only provided suggestion for Selenium 2 / WebDriver. Unless the OP mistyped version.
If I'm not mistaken, Selenium RC automatically handled frames and iframes w/o need to switch to it, at least it was the case for us. We only started needing to do so after moving to WebDriver. RC found and treated content in iframe as on same page/frame as main page in RC for us.