I believe to get the presentation like on the Mather HS site you'll need to use Keynote 08 and export the presentation as a flash presentation. Then embed it in the page with an HTML snippet and iFrame code.
Keynote 09 dropped flash from it's features. This demo page has a Keynote presentation embedded as a Quicktime Movie:
Keynote Presentation in iWeb.
A flash presentation from Keynote is on this demo page:
adding Flash with iFrame and HTML snippet
As I recall the send to iWeb method creates an html version of the presentation which does not support the fancy transitions that Keynote is capable of.
Happy Holidays