While working at a customer site a couple of users reported Word 2007 has no page number gallery when you go Insert -> Page Numbers. After investigating I found that just deleting the Building Blocks.dotx file in their profile fixed the problem.

Windows XP Location:
c:\Documents and Settings\{your username}\Application Data\Microsoft\Document Building Blocks\1033\Building Blocks.dotx

Windows Vista & 7 Location:
c:\Users\{your username}\AppData\Roaming\Microsoft\Document Building Blocks\1033\Building Blocks.dotx