Since upgrading to Mac OS X 10.6 we've lost the ability to use the right-click contextual menu item to scan files and folders with NAV. This is because the Finder is now a 64-bit application and cm plugins are not supported by 64-bit apps (see here for further info).
Here's my solution / workaround using the new Services feature in OS X 10.6:
1. Launch Automator (from your /Applications folder)
2. Select 'Service' in the "Choose a template for your workflow" dialog
3. Set the 'Service receives selected' option to "files and folders" and change the application to "Finder"
4. In Library pane on the left select the Files & Folders category and then locate the 'Open Finder Items' action. Drag the action over to the right-hand pane to link it to your existing 'Service'
5. In the 'Open Finder Items' action change the 'Open with' application to the "SmallScanner" application which is part of Norton AntiVirus for Mac. You will find it in \Library\Application Support\Symantec\AntiVirus\ folder (note this is located in the Main Library on your OS Boot Drive, not your user ~\Library folder)
6. Save the Service as 'Scan with NAV' or whatever you want to call it.
That's it. Give it a try. Select one or more files/folders in the Finder, right-click goto Services and then select 'Scan with NAV' or whatever you called your new service. The Service will pass the selected files to the NAV 'SmallScanner' application which will scan them and show a status dialog with the results of the scan, all without having to launch the main NAV application.
Cheers,
Stu