Vijay,
From 815 and up try this...
1. write a java class.
2. write a fxn in oracle
here's the code...
Code:
SQL*Plus: Release 8.1.6.0.0 - Production on Mon Aug 26 16:20:09 2002

(c) Copyright 1999 Oracle Corporation.  All rights reserved.


Connected to:
Oracle8i Enterprise Edition Release 8.1.6.0.0 - Production
With the Partitioning option
JServer Release 8.1.6.0.0 - Production

[email protected]>create or replace JAVA SOURCE
  2  NAMED "MyTimeStamp"
  3  AS
  4  import java.lang.String;
  5  import java.sql.Timestamp;
  6  
  7  
  8  public class MyTimeStamp
  9  { 
 10  public static String getTimestamp()
 11  {
 12  return (new Timestamp(System.currentTimeMillis())).toString();
 13  }
 14  };
 15  /

Java created.

[email protected]>create or replace function my_timestamp return varchar2
  2  AS LANGUAGE JAVA
  3  NAME 'MyTimeStamp.getTimestamp() return java.lang.String';
  4  /

Function created.

[email protected]>col my_timestamp format a25
[email protected]>col normal format a25

[email protected]>select my_timestamp, to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') normal
  2  from dual;

MY_TIMESTAMP              NORMAL
------------------------- -------------------------
2002-08-26 16:42:37.226   2002-08-26 16:42:37
It's also possible to do in 8.0.

Cheers!!!

Tarry