I need to enter a banner with iframe code in my website. That's the form I need to use (it's from a company).

It begins like this

<iframe id='a90a5171' name='a90a5171' src='http://

etc.

it ends like this:

</a></iframe>

How exactly am I going to put it on my website? I want it to appear at the header of index. I'm using Joomla 1.5.10 , Legacy 1.0

Please describe me the procedure step by step on where to click. I tried the Component-Banner menu and then the Module Manager but I couldn't use the banner either way.