Was personally having this issue in Word 2007 where the Print Preview displayed the background image correctly, centering and filling the entire background, yet printing to a PDF or printer results in the background image being tiled repeatedly on the entire page ==> finally figured it out!
Since the Header formatting option presented by others typically is not an appropriate option for many encountering this issue, and the background printing/spooling options don't work, the resolution to prevent the background image from tiling when printing to a PDF or a printer is as follows:
• Open the document in Word 2007
• Click on the 'Page Layout' tab
• 'Page Background' section > click 'Page Color' > click 'Fill Effects...'
• 'Fill Effects' window opens > click 'Texture' tab > click 'Other Texture...' button
• 'Select Texture' window opens > navigate to and click on the desired background image > click 'Insert' button
• 'Fill Effects' window opens > click 'OK' button
Since there is a known issue between MS Word and some print drivers resulting in pictures in the background being tiled instead of centered and filled, the trick is to insert the background image as a 'Texture' instead of a 'Picture'. Save your Word document and then edit as needed for any content to be displayed on top of the background image.
~ Bruce
Note: I see that JML had a virtually the same resolution back in Apr 2011, so this post is just more detailed.