There is no search function currently offered in in5. The implementation of a search feature has been on the Ajar wishlist for sometime. As with all features, we strive to introduce features that provide a useful and robust solution, so finding the proper approach to an ideal search function is an ongoing endeavor.
As far as search within an iframe, it's generally not doable. I'm not 100% sure on the WP-specific search, but due to how iframes retrieve and deliver content, I would guess that it's not possible. Even search engines tend to skip over the content on the page containing the iframe.