I am trying to prevent my users from entering a comma or dash in an address data item field on a form. Can I create an expression in the properties ValidationText box to do this, or do I need to do something else?

Any help would be appreciated!!

Using the code in this article you can strip the unwanted characters from the strings that your user enters by placing the code in the After Update event of the text box.
http://support.microsoft.com/support/kb/articles/Q138/7/74.asp?LN=EN-US&SD=gn&FR=0