[WIN32] Quiet install and changing defaults

Hello:

I am attempting to override the default installation directory that the
postgres MSI uses. I'm not familiar with MSI, but from what I've read I
can specify properties on the command line to change properties in the
installer? I've tried a variety of properties from looking at the
installation log and by examining the properties using the ORCA tool
from Microsoft. All to no avail:

msiexec /i postgresql-8.1.msi SOURCEDIR=[my directory]
msiexec /i postgresql-8.1.msi TARGETDIR=[my directory]
msiexec /i postgresql-8.1.msi DEVDIR=[my directory]

In all cases the installer still presents me with the default directory
(c:\Program Files\Postgres8.1) and not the one I specify on the command
line. Should some combination of the above work?

My final goal is to be able to spawn the pgsql installer from my
installer and override defaults for the user and password and
installation directory. Is this feasible?

Hopefully this is the right list, if not if someone could direct me to
the correct one, I'd appreciate it.

Please CC me as I am not currently subscribed to this list.

thanks

-- chris