PostgreSQL: The database cluster initialization failed
I had the same issue installing 9.1.4 on Windows 7. I managed to find a solution online that worked.

The steps I followed are:


Uninstall PostgreSQL
Delete the postgres user if it still exists. 

net user postgres /delete

Create the postgres user with a password you can remember

net user /add postgres &lt;password&gt;

Add the postgres user to the Administrators group

net localgroup administrators postgres /add

Add the postgres user to the Power Users group

net localgroup "power users" postgres /add

Run a command window as the postgres user

runas /user:postgres cmd.exe

Run the install file from within the command window.

C:\Download\postgresql-9.1.4-1-windows.exe


This should run the installation successfully. 
Remove the postgres user from the Administrators group.

net localgroup administrators postgres /delete