1. In the <iframe></iframe> tag use "allowtransparency=yes" that will allow any background image on the main page to blend into your iframe in both Firefox & IE.
2. In the <iframe></iframe> tag, set name=iframe. Then when creating links, link them to the iframe frame. This will change the page.
For example:
<iframe src="home.html" name="content" allowtransparency="true" height="340"width="530"></iframe>