[root@www ~]# su - oracle
[oracle@www ~]$ echo $ORACLE_HOME
/home/oracle/oracle/product/10.2.0/db_1
[oracle@www ~]$ sqlplus system@iamtrying

SQL*Plus: Release 10.2.0.1.0 - Production on Sun Apr 11 13:37:14 2010

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

Enter password:
ERROR:
ORA-12154: TNS:could not resolve the connect identifier specified


Enter user-name: