I have some problems while installing PostgreSQL

Dear all

I try to install PostgreSQL on WindowsXP (Professional Ed). Unfortunately, I
could not complete install process because there are two errors at copy new
file stage.

1. At the first time of installing, the error said "Internal account
lookup failure: No mapping between account names and security ID was done".
I have no idea to fix this error. How this error comes from? Then,
installing process rolls back.
2. At the second time, I tried to install it again. At this time, the
error said "xxx user name already exists" and rolls back again. I wonder
that because the first time installation failed, why my username still be
remembered. How to fix this error? There is no PostgreSQL folder in Program
Files directories.

My computer is running Tomcat 5.0.28 while I do installing. I am not sure
whether it related to the errors or not.

Therefore, I wish to ask you how to solve these problems. Thank you in
advance.

Mr. Kraisak KESORN