After install, several addition files are also saved on your system (for Vista there is a shortcut on desktop and files are actually in public download folder)
.
The install file changes (Symantec is tricky here—I suspect it is the dll: NIS2010plugin.dll that is also downloaded) and when you open it AFTER INSTALL, there are options to uninstall NIS2010—NOT to install.
But there is also a text file: downlaodinfor.txt that contains the new key and a URL to load if you need to re-download the install for 2010.
I asume Nav alsoworks the same way.