Unfortunately, sometimes CABs are created which are uninstallable. This happened to me one time on the same program. I ended up having to manually uninstall the program by deleting the files installed and the registry entries installed.
Files that need to be uninstalled:
\Program Files\SprintNav\SprintNav.exe
\Program Files\SprintNav\telenavresource.bar
\Program Files\SprintNav\Preferences.bin
\Program Files\SprintNav\TeleNav.cfg
\Windows\TelenavPlugin.dll
\Windows\Start Menu\Sprint Navigation.lnk
Yes, you can just delete the SprintNav directory
Registry entries that need to be uninstalled:
[HKCU\Software\TeleNav]
AppPath = "\Program Files\SprintNav\SprintNav.exe"
OSVersion = "5.01 - 5.99"
Yes, you can just delete the TeleNav key.
After which, you should be able to install no problem.