- go to $ORACLE_HOME/bin, 
- type emctl status dbconsole 
- Got error msg 'Environment variable ORACLE_SID not defined. Please define it.
- type SET ORACLE_SID=DEV10G3
- type emctl status dbconsole
- Got error msg 'EM Configuration issue. c:\oracle\ora10g3/10.10.10.11_DEV10G3 not found.' (btw, 10.10.10.11 is the IP address I assigned to my Microsoft Loopback Adapter).
- I created the directory named in the above error msg
- type emctl status dbconsole
- Got error msg 'OC4J Configuration issue. c:\oracle\ora10g3/oc4j/j2ee/OC4J_DBConsole_10.10.10.11_DEV10G3 not found.'
- But I do see existing directory c:\oracle\ora10g3/oc4j/j2ee/OC4J_DBConsole_blackbird_DEV10G3 (blackbird is the host name of my machine). This directory has lots of subdirectories and files in it. 
This gives me the necessary 'AHA!!!!', so I go to c:\windows\system32\drivers\etc\hosts and add an entry equating 10.10.10.11 with blackbird.
- type emctl status dbconsole again. Now I get: 'Oracle Enterprise Manager 10g is not running.' 
- type emctl start dbconsole
- IT WORKS!

E:\>set oracle_sid=catdb

OC4J Configuration issue. C:\oracle\product\10.1.0\Db_1/oc4j/j2ee/OC4J_DBConsole
_alwarid-taj.fakhruddin.local_catdb not found.


after go DBCA and configure database with Enterprise Manager.

E:\>set oracle_sid=catdb

E:\>emctl status dbconsole
Oracle Enterprise Manager 10g Database Control Release 10.1.0.2.0
Copyright (c) 1996, 2004 Oracle Corporation.  All rights reserved.
http://alwarid-taj.fakhruddin.local:5502/em/console/aboutApplication
Oracle Enterprise Manager 10g is running.
------------------------------------------------------------------
Logs are generated in directory C:\oracle\product\10.1.0\Db_1/alwarid-taj.fakhru
ddin.local_catdb/sysman/log

As root user
#xhost +
As oracle user
$export DISPLAY 127.0.0.1:0.0

as root user
linux@root]#xhost +
as oracle user or normal user 
linux@oracle]$export DISPLAY="127.0.0.1:0.0"
if above is not working then
linux@oracle]$export "DISPLAY=:0.0"