You probably could, but as far as I know, iWeb is like the Frontpage of Mac? I have never really opened it on my Macbook, to be honest.
If you really want to get into web development, I suggest you stay away from editors like iWeb, Frontpage, even Dreamweaver (my personal opinion).
I would advise you to pick up some books or follow some basic tutorials and work with a decent IDE (Aptana, ..) or code editor (I'm thinking Textmate, Coda, ...).
This NetTuts screencast is entirely dedicated to choosing an editor. Perhaps that helps you!
Edit: Since you're new to webdesign, and I ran into another question regarding 'being new' a couple of minutes ago, I'm also going to tell you the same as I told the other person: stay away from w3schools. It's evil.