iFrame stacks or plugin doesnt do what i thought it would?

Hi All, in a few of my site pages i would like to display another Site.

I have pasted this other sites web address into different iFrame stacks/plugins but when Previewed this other web site takes over the whole page, removing the Banner, Header, Menu and Footer, leaving no sensible way of getting back to my Site.

I always thought that this other site would simply be displayed in my Sites Main Content area, in between the Banner, Header, Menu and Footer.

Or is there something else i have to do to get the effect i am hoping for ?