Helen,
You have received lots of suggestions. However, I think the primary cause of Stuffit crashes on launch is that it attempts to check a web site for newer versions. What you need to do is disable this feature. Disconnect from the network (or turn off Airport) and then launch Stuffit Expander (or whatever Stuffit product is giving you trouble). In the Preferences for Expander, locate the option to allow version checking and uncheck it. Problem solved.
bd