Are you serving the Word or Excel apps from the server? If so, it sounds like you may have a sharing error. Something that can help in this is to install Dr. Watson on the server (if it is throwing the errors) and the workstations. Dr. Watson (Google: Dr. Watson AND Microsoft) is a Windows error debugger. This will give you a dump of the error, the memory locations and applications that are causing the problems. It will make it easier to find the core issue.

This, of course, assumes that you have a current anti-virus, firewall and all that installed and running, and you have already checked the Word and Excel files for Wazzu and other macro virii?