We check registry keys to see if PostgreSQL has been installed. If it was installed previously for another program sometimes those keys can be left behind. PostgreSQL is required for PT4 to work, so if you don't have it you will need to install it.
For 64 bit windows you want to use PostgreSQL 9.0.11 from
here.
For 32 bit windows you want to use 9.0.11 but with
this installer.
If you're not sure, try 64 first - if it installs you've got 64 bit windows. If you don't it'll tell you that it won't work during the installation and you can delete the installer and then grab the 32 bit version.
After you install it, in that configuration window use whatever password you entered during the installation process (dbpass is just our default, and you can use that one if you like to make things simpler) and then you should be able to connect and proceed from there.