pq_shadow

I am writing you because I am new to Postgesql and I have encountered a problem that I have not been able to solve through your doc's or mailing list.
The problem is with the createuser utility. When I try to create a user I get the following error:

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[root@crescent1 root]# createuser webmaster -P
Enter password for user "webmaster":
Enter it again:
Shall the new user be allowed to create databases? (y/n) y
Shall the new user be allowed to create more new users? (y/n) y
psql: FATAL 1:  SetUserId: user 'root' is not in 'pg_shadow'
createuser: creation of user "webmaster" failed
[root@crescent1 root]#
##################################################################

I would like to be able to use Postgresql (not just Mysql) but if I can not create a user I can not login to the Postgres data base. I advise me on how to fix this problem. 

I am using Red Hat 6.2 on a Intel based x86 with a Pentium CPU.

Eric Williams