check the otn.oracle.com link

iSQL*Plus is automatically installed and configured. The URL for your iSQL*Plus server is:

http://your_machine/isqlplus

If this URL does not display the iSQL*Plus login page, check that the line in the Oracle HTTP Server configuration file that includes a reference to the isqlplus.conf file is uncommented. The Oracle HTTP Server configuration file can be found at:

%ORACLE_HOME%\Apache\Apache\conf\oracle_apache.conf

If it is commented out, removed the '#' and restart the Oracle HTTP Server.