Postgres ODBC driver 8.04 installation recovery path

Greetings!

I want to install the Postgres ODBC driver version 8.04 for a customer
that is currently using 8.01. However, I cannot make any change to the
customer's computer without being able to undo the change in case
something goes wrong. The customer has a spare computer that we have
been using as a testbed. That machine already has 8.04. I uninstalled
it. I am trying to install 8.01. The installer reports that it
completed successfully, but the driver is not in the list of choices
when I call up the DSN configuration box.

My ideal situation would be to have the two versions installed side by
side. If I could do that, I could test my program against the old
driver, see the problem I am trying to fix, change the DSN to use the
new driver, see the problem go away, and uninstall the old driver.
However, side-by-side installation does not seem to be possible. My
question about how to do it received no replies.

So, I need a reliable way to uninstall the 8.04 driver and re-install
8.01 so that I can assure the customer that if something breaks, I will
be able to fix it. How can I do that?

Thank you very much!

RobR