Prudhvi,
Thanks for providing the @@version info as that allows me to provide you
with a solution to error . Basically, this is a FTS component or registry
key issue, that cannot be resolved by detaching & re-attaching the database
as this problem is at the SQL Server level and not database specific.

What you must do is to "re-install" the SQL Server 2000 Full-text Search
components via your SQL Server 2000 setup CD. As the FTS components are
already installed you will need to force the removal of the FTS installed
checkmark via the removal or renaming of the following tracking registry
key. (If you're not using a named instance, remove "<Instance_Name>\".)

NOTE: be sure to be logged on to the server as either Administrator or as a
member of the server's Admin Group before deleting the below registry key
and stop both the MSSQLServer and the MSSearch services.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL
Server\<Instance_Name>\Tracking\
{E07FDDA7-5A21-11d2-9DAD-00C04F79D434}

Once you're done removed (renamed) the above tracking key, then delete the
MSSearch directory from either:

drive_letter:\Program Files\Common Files\Microsoft Shared\
or
drive_letter::\Program Files\Common Files\System\

Then using your SQL Server 2000 installation CD re-install via "Custom
Installation" the Full-Text Search component (it should be un-checked). When
this completes find and save these files: SearchSetup.log (usually under
\windows or \winnt folders) and sqlsp.log. If any problems, please post
these files.

Re-install the service pack that you may have applied to SQL Server 2000, so
that the newly re-installed MSSearch components are upgraded to SP3 levels
and then re-boot &/or restart the MSSearch and MSSQLServer services.

You may also want to consult or perform the procedures document in the
following Kb article: 827449 "How to manually reinstall the Microsoft Search
service for an instance of SQL 2000" at:
http://support.microsoft.com/default.aspx?scid=kb;EN-US;827449

Hope that helps!
John