How do I mix landscape and portrait in the same document?

In Pages 3.0 you cannot mix portrait and landscape layout within the same document.

One way of simulating mixed page orientation is to use a rotated text box on the pages where you want a different layout.

If that does not suit your needs you may want to try NeoOffice/OpenOffice. First define one Page Style for landscape and one for portrait:

1. Format > Styles and Formatting > Page Styles (icon over the list of styles).
2. Create new styles or right click on existing Page Styles to Modify their properties. Orientation is under the Page tab.
   
3. Put the cursor where you want to change page orientation.
   
4. Format > Paragraph > Text Flow. (I did not name those menus. I just copy their names. Don't blame me!)
   
5. Set Breaks > Insert. Type: Page.
6. Click on With Page Style, and select a page style with portrait or landscape mode.

Or in MS Word:

1. Format > Document. Apply to: "This point forward".
2. Click on Page Setup... and change to landscape or portrait.