If what symantec told me is true all the vplogon.bat file does is check the value of a registry key which can be done by checking for a valu of..
code:
  
"HKEY_LOCAL_MACHINE\Software\Symantec\InstalledApps","NAVCEClientNUMBER"
If that key isn't there here's how I install NAV..
code:
If @INWIN = "1"
  Shell "\\navserver\vphome\clt-inst\win32\INSTMSIW /Q"
Else
  Shell "\\navserver\vphome\clt-inst\win32\INSTMSIA /Q" 
EndIf
Shell "%COMSPEC% /C START \\navserver\vphome\clt-inst\win32\NAVCE.MSI REBOOT="+Chr(34)+"FORCE"+Chr(34)+" /QN"
The first part checks the windows installer, installs it if needed, it then loads nav and reboots automatically after the installation.

L8tr...