Finally plucking up the courage to find out how to do this, I found one page (no doubt of many) that tells you how to achieve this -
http://www.castlejb.com/webdesign/landscape/landscape.html
It's actually pretty easy - just define new section breaks and format those sections the way you want them! In MS Word 2010 it's a bit different to the instructions listed here;
- Select the beginning of the section to format
- Page Layout
- Breaks => Next Page
- Go to the end of the section to format
- Page Layout
- Breaks => Next Page
- Then select the section and go to Orientation => Landscape / Portrait
Voila!