Hi,
I need to develop a piece of script in PL/SQL to bring up a Password
and Username box, which functions. can you please help with this?

No can do.  PL/SQL is not a GUI based language, there is no GUI.  It
is code that runs on the server.  To run it you must be logged on to
Oracle which means you already logged on and hence asking to log on
doesn't make sense.  You can go to www.otn.oracle.com and sign up for
free (no spam) and read the documentation.

Are you by any chance trying to use the PL/SQL web toolkit to build a
HTML login application?

Checkout this link with example for PL*SQL ACCEPT command
http://otn.oracle.com/support/tech/sql_plus/htdocs/command.html


ACCEPT variable [NUMBER|CHAR] PROMPT text NOPROMPT HIDE
accept variable_user prompt 'UserName : '
accept variable_pass prompt 'Password : ' hide


This won't bring up a "GUI" box but  might be what you are looking for.