Highlight your text and right click, chose 'paragraph'. There'll be an option for line spacing i.e. 1, 1.5, and there's also a before and after spacing. Make sure they're at 0pts. I'm using Word 2003 but it should work the same. Hope that helps.
Finally worked out that there were some rogue footnotes in there- I'd deleted them in the notes but not in the body of the text so they were just coming up as gaps. Thank god I realised! Anyway, work is IN and I'm going to lie down in a darkened room.