Installation on XP

Hi,

I am trying to install postgresql-8.0.1 on a machine running XP
Professional.
On the web site I went to the download area, then to V8.0.1 and then
to win32.  I downloaded postgresql.8.0.1.zip .  I unzip that and executed
postgresql-8.0.msi .  When I hit the "Start" button, I get the following:
    This insallation package could not be opened.  verify that the
package ....

I cannot seem to find any way to get past this problem.  Did I just miss
something simple?  Any Help?

Thanks,
Glenn