From the NPM homepage, go to 'settings->Network Sonar Discovery'
The Network Sonar Wizard will display. On the SNMP credentials page, enter all the known SNMP credentials for the devices you want to discover. You can repeat this action.
Once added, 'Next' through all the other selection options as appropriate (VMWARE, add to NCM or Windows credentials) and then define your network ranges under the Network selections.