[quote]do you have any sample code how to interact oracle using kerberos via DOA.[/quote]
I have no personal experience with Kerberos, but the process of configuring Oracle Net for Kerberos Authentication is explained in the "Oracle Advanced Security Administrator's Guide", and the way I understand it is that it is transparent to Oracle Net applications (such as your Delphi application). The user connects without specifying a username/password, and instead Oracle Net uses the Kerberos ticket on the client machine.
[quote]one more thing we have D7 license for DOA components. when we upgrade to xe2 or higher do we need to pay for DOA upgrade?[/quote]
If you have a 4.1 license then you can use any Delphi version, including XE2.