Sure NetBackup 6.0 is a bit old, but its enterprise software, so having the latest and greatest version is not always feasible. As such the install script will show errors as the program depends on some old libraries not installed by default.
First install the needed library: compat-libstdc++-296 Then run the install script and you should not see any errors about missing libraries.
Next up is xinetd. NetBackup 6.0 was built using the older inetd, but xinetd supports importing old config scripts.