Check out these links. http://www.w3schools.com/tags/tag_iframe.asp http://htmlhelp.com/reference/html40/special/iframe.html http://en.wikipedia.org/wiki/IFrame
<iframe src="http://www.nameofsitehere.com/nameofpage.html" width="400" height="400" frameborder="0"></iframe>
Just thought I would let know that SE cannot read content within iframes, they just link to the page insted. They can be appropriate in some situations such as a banner, but not to structure a website as this would cause many accessibility issues and would result in a poorly structured website, and would not be sematically effective.
Very true iframes are not the greatest for SEO... I would prefer PHP tables instead! They're more SEO friendly
I've got to agree totally, W3 is and absolutley great site, for all coding languages and syntaxes! But it is true, iframes mean that Search Engines won't be too happy and you also can't really put most content based ads into an iframe... Diarmuid