packaging issue / upgrading with psql-odbc msi packages 8.03.01.00

I'm trying to create an nsis installer package for deploying software that
uses pgsql and the pgsql-odbc driver
I wish to un-install all previous versions of pgsql-odbc and install the
latest version.

in testing when installing 8.03.0100 over the top of 8.01.0200
double clicking on the msi file- replaces/upgrades the driver to 8.03 .01.00
but leaves the add/remove programs entry

running upgrade.bat, completes but does not do anything
( msiexec /i psqlodbc.msi REINSTALLMODE=vamus REINSTALL=ALL /qr )

modifying upgrade.bat, upgrades drivers, does not remove add/remove programs
entry
( msiexec /i psqlodbc.msi REINSTALLMODE=vamus /qr )

differently modifying upgrade.bat, does not install
( msiexec /i psqlodbc.msi REINSTALL=ALL /qr )

Is this desired functionality of the msi install? (i.e. do i have to
manually somehow detect previously installed verions and uninstall them
programatically)
Or is the current msi supposed to detect and remove previous versions /
overwrite previous version and remove the add/remove programs entry.

thanks for your help, sorry if what i am trying to do looks like a hack
(sometimes things really are as they appear!)