Word errors when using underline & tabs

I have Office 2000 running on a variety of PCs. One issue with Word 2000 we have is when a user is creating a legal document, word will shut down unexpectedly. The situation where this occurs happens when a user creates an underscored area on a line, then sets a tab (left tab for example), tabs over to the newly created tab, and then underscores to create a second line..all on the same line. In almost all cases if the user uses the underscore too far and hits the right margin, word 2000 generates an error and shuts down. Any ideas???