installation fails during postgreSQL phase on XP SP3

I am trying to do an install of PostBooks - downloaded from SourceForge - on an XP SP3 machine and it repeatedly fails with two error messages:

1) C:\Documents and Settings \(my user name)\Local Settings\Temp\postgresql_installer\validateuser.exe "." "postgres" "****"

2) C:\Documents and Settings \(my user name)\Local Settings\Temp\postgresql-9.1.2.1-windows.exe -mode unattended -superpassword (mypassword) -servport (port)

In both cases, the rest of the message says the program returned an incorrect code. The first message sticks around on screen for a few seconds and is replaced by the second message. When you click on OK, the installation terminates.

I have tried installing in C:\xtuple, as suggested by another thread. i tried changing the port, in case there was a conflict. No help. I do not have PostgreSQL installed on this machine - except that like every machine around here, it is configured as a web server, and Apache brings in some "stuff" related to PostgreSQL. But no services are running for it. I did a search in the registry for anything realted to PostgreSQL and other than the apache related keys, there isn't anything.

I'm pretty much just taking the defaults for everything in the installation dialog, except for seeing if changing the port number would help.

Any suggestions on how I can make some progress here?

Before anyone suggests it, since I develop database-driven web apps for a living, the idea of removing the web server software is a non-starter.