I wish I could offer some insightful help. MS Word is super crappy on all of the OS X machines I've used. Just a genuinely poopy piece of bloat-ware. Sorry to hear, but not surprised, that its no better under Leopard.
Mine done the same thing if I used the "Spotlight like" search box under the help menu, but if I opened the help window in Word and searched it didn't crash. It's possibly a fluke with Word/Office for Mac.
Also, anyone know how to fix the toolbars on Word (and Excel) so that they follow more like Windows? These bars are not fixed to the program and you can't lengthen them. I end up accidently going to other programs I have open that are "behind" Word cause the tool bar doesn't cross the entire screen.