First you will need the basic iframe code. This is what i'm using:
Open up MS paint. For this tutorial i will be coding this example layout which i made in 5 seconds :) You can use it aswell if you like.
Use the selection tool to select the content box of your layout.

Dont let your mouse go. Now look at the numbers on the bottom of your paint window. If you don't think you can remember them just take a screen shot or write them down. Heres where the numbers will go on your code:

Now add in your numbers to the right sections of the iframe code. Mine would be as follows:
left:48
top:106
width=382
height=260
So my new iframe code would be:
Hope this tutorial helps;D Any questions send me an email or tag!