You can use an iFrame gadget to embed another web page in your Google Sites web page.
For Example: https://sites.google.com/a/aea267.k12.ia.us/schma3-duplicated/iframe-test
On the page where you wish to embed the external web page:
Edit Page -> Insert -> More Gadgets ->
Make sure and select Featured ... and select the 'Include gadget (iframe) and then select again.
Edit the 'Properties' of the gadget and include the URL to the page (e.g. http://www.aea267.k12.ia.us) that you'd like to embed into your Google Sites web page.
I would suggest at least 800. I would also suggest that your iFrame always have a width of100 PIXELS and be used only on pages that are single columns, not two column layouts.