Conditional automated installs under Windows

Hi Folks,

I apologise in advance if this is a little off-topic for this
group, but it's as close a match as I could find.

I am developing a script/bat that is intended to ensure
that a PC on startup has a designated level of Mozilla
installed.

I have unpacked the installer file ito its constituent bits
and think I can see how I use initool.exe to set up the
installation prior to running "setup -ma" switch.

I have read that I need to uninstall before updating,
and that %SYSTEMROOT%MozillaUninstall.exe is
used to so this.

Obviously I would like to only uninstall and update if a
newer version is to be installed.

How do I compare the version I am about to install
with what is already on the PC?  I assume that there
must be a way of comparing the mozver.dat file in
%SYSTEMROOT% with something in the files that
comprise the setup bundle, but I can't see how.  I
was not able to get "setup.exe -?" to show anything.

The version I'm testing with is 1.2.1.

Cheers, Dieter.