Defining 'C' functions in Postgres

Hello
I am using Postgres for the first time. I tried to define a 'C' function
in Postgres using the CREATE FUNCTION command but encountered the
following:

 ERROR:  Only users with Postgres superuser privilege are permitted to
 create a function in the 'C' language.  Others may use the 'sql' language
 or the created procedural languages.

The command is
 CREATE FUNCTION phone_in(opaque)
 RETURNS phone
 AS '/home/M97/acs/vassilik/protein/phone.o'
 LANGUAGE 'c';

It is not me that installed Postgres. Is this the problem?

Kostas Vassiliadis