If you are running ArcInfo 7.x, your arcexe7x folder will not be overwritten. By default, the installation procedure will create a folder called arcgis. Before installing ArcView 9.1, you must uninstall 7.x UserSetup. Refer to the appropriate ArcInfo 7.x installation guide for instructions to uninstall UserSetup.
It is possible for a 7.x network server installation and a 9.1 network server installation of ArcView or ArcInfo Workstation to exist on the same machine. However, client installations of both versions cannot exist on the same machine.
Before installing ArcView 9.1, you must uninstall ArcView from Add/Remove programs.
Before installing ArcView 9.1, you must uninstall all ArcGIS 9.0 products from Add/Remove programs.