Publish your calendar online from iCal. Then visit it and get its URL.
In the snippet add the URL to the iFrame code and set the width and height as needed.
<iframe height="XXXpx" allowTransparency="true" frameborder="0" scrolling="no" style="width:XXXpx;border:none" src="URL OF YOUR ONLINE ICAL CALENDAR"></iframe>
Again, if the iCal is too big for your iWeb page consider going the Google calendar route and use Spanning Sync to keep the Google calendar synced/identical with your iCal calendar as I've done on my demo page:
Google calendar.