ident authentication problem

Hello
I am newbie to postgresql I have to make project using this . I am learning it but at every step i am getting error .
now I am stuck with the error

-bash-3.2$ psql -d xnat -f sql/xnat.sql -U xnat
psql: FATAL: Ident authentication failed for user "xnat"

I have made changes in my pg_hba.conf file also but then too this error is coming
Plz someone help me to get rid of this .

Thanx
Regards
Madhu Harchandani

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