I am still trying to get to grips with Office 2007 and have certainly found it less stable than 2003. I’ve not encountered your problem (lots of others but there we go!!) but one question: have you got service pack 1 installed?
If not, it’s worth trying.
Other thoughts are:
under resources you could run the diagnostics;
or exit Word, find your Normal.dot file, call it Normalold.dot and restart Word which will recreate a new Normal.dot file (the corruption of which often gives problems). This will remove any macros or personal settings you may have. If the problem is not solved, you may want to go back to your original file to recover the macros etc.