Cannot upgrade to 8.4.1 on Windows

I am a PostgreSQL novice. I successfully installed 8.3.3 on a Windows
XP Pro machine using the pgInstaller and have been using it since. Now I
want to upgrade to 8.4.1.

The only installer I can find for Windows for 8.4.1 is the One Click
installer provided by EnterpriseDB. If I attempt to run the One Click
installer while logged on as the postgresql user it fails immediately by
displaying the infamous Windows dialog that says the program has
encountered an error and must be shutdown and asking if you want to
send a report to Microsoft or not.

Thinking that this might be a rights issue I added the postgresql user
to the Administrators group and tried the install again. This time a
dialog appeared stating that the Microsoft C++ RTL installer had
encountered an error. The dialog then disappeared. In both cases the
installer never reached the point of displaying its splash screen.

Next, I tried running the installation under my normal login, which is
also a member of the Administrators group, and it ran. Of course the
installation it created is unusable because PostgreSQL now runs under my
account, the postgres database does not exist, a database with my
account name was created and I am sure other things are messed up also.
Therefore I uninstalled 8.4.1 and deleted the installation directory.

Is there a complete set of instructions for installing 8.4.1 on Windows
somewhere? I have not been able to find anything using Google and the
information in the manual is incompatible with the One Click installer.
If there is no accurate documentation can someone suggest what I am
doing wrong? Thanks.

Bill