Yes. It's actually fairly easy once you get the hang of it.
First you want to create your iframe...
CODE
<iframe src="THE URL OF WHAT DEFAULT PAGE YOU WANT THERE" width="WIDTH" height="HEIGHT" scrolling="auto" name="main"></iframe>
There are many different ways you can make an iframe but that is basically the easiest, IMO.
Example:
CODE
<iframe src="http://www.yoursite.com/index2.html" width="500" height="500" scrolling="auto" name="main"></iframe>
That creates the actual iframe - PUt that where you want your iframe to go.
Now, as for the links.. The default basic link of most people is
<a href="http://www.thissite.com/thispage.html"> text here </a>
But.. You want to add the SRC tag to that so that it tells the link WHERE to put the page.
<a href="http://www.yoursite.com/thispage.html" src="main"> text here </a>
You want the SRC to = whatever the name of the iframe was.. That will make the page load in the iframe.
And there u go.
P.S - By the way.. If you ever want to load a page in a new window, you just give it an SRC of something that you don't have a frame of.. But most people, including myself just give it "_BLANK"..
<a href="http://thissite.com/thispage.html" src="_BLANK"> text here </a> That will open a page in a new window.