Moving to Office 2008 will probably fix the problem.
2004 had no idea what a 2 core processor was, let alone an 8 core.
Alternatively, move to Open Office or iWorks.
Oh yes, I would also suggest that you do not leave 2004 running when it is not needed.
I have had this problem intermittently for about 3 years. Microsoft Word 2004 causes all 8 cores to hit 100% and get very hot, strangely when this happens it doesn't seem to trigger a fan in the mac pro. Luckily I have a software program at the top of the toolbar that constantly gives a visual display of both activity and temperature of each core. I'm concerned that some nights I go to bed and Word is still open, if not causing damage, possibly at least shortening the lifespan of the cores. There is no question Word is involved, as soon as I quit (usually have to force quit)the cores return to normal idling and cool down. Any ideas?
All software current-Mac pro 2007 8 core intel 9gb RAM, OSX 10.6.4