Installation problem

My installation has stalled with the following message:
"User 'postgres' could not be created. The user account already exists!"

Initially I had problems providing a suitable domain name and password. So, I have made several attempts at installation.

How do I now proceed to install successfully?

I used postgreSQL during a recent contract position, and I am impressed by its capability and the maturity of the product. I hope that I can resume my expereince soon.