[CentOS] postgres 7 - CentOS 4.4

Hi

Firstly apologies but i have to install an app that uses postgres but i 
am more a MySQL/Oracle guy so i maybe doing something really wrong here..

I am following instructions for creating a DB user and encountering this

# createuser -ADP -U postgres foo
Enter password for new user:
Enter it again:
createuser: could not connect to database template1: FATAL:  IDENT 
authentication failed for user "postgres"

In a standard postgres install whats causing this? I presume its because 
the user postgres has a pwd but what is this and why am i not being 
prompted to enter this?

Thanks and apologies as i know this is not directly a CentOS problem