If you have the complete Workbench 3.1 set installed, then copy the CD0 and CD0.info files found in SYS:Storage/DOSDrivers to SYS:Devs/DOSDrivers. Edit the CD0 file to use gvpscsi.device as device driver and set the unit number to the one on the CD drive. Now write Mount CD0: and everything should be ready to go.
