How do I make a drop down list visible and invisible in a grid, based on the selected value of another drop doWn list -PLEASE READ THE WHOLE QUESTION

Hi!
I have a grid view consisting of about 7 columns namely, treatment reason, treatment id, status code , letter code , etc Treatment reason , treatment id, status code, letter code have drop down lists.treatment id drop down list populated by the values from a table and contains values such as 1, 2, 3.

when treatment id "1" is selected, a value from the status code drop down list must be selected ,
otherwise, the drop down list needs  to be hidden from the user, when adding a row or updating a row.
or the user should not be able to select any status code when treatment id is not "1".

Can anyone help me accomplish this ASAP USING ASP.NET AND C#2.0

It's very urgent. If i can get the logic/ code , that'll be grrreat.

I have one more question.
I have a table which ha sthe following columns
Treatment reason id pk, fk, not null
treatment id,pk, fk, not null
status code,pk, fk, not null
letter code fk not null
ttp null

treatment reason id, treatment id , status code constitute composite primary key.
as mentioned above, the user must select a status code only when the treatment id is "1", otherwise,
status code should be stored as an empty string in the sql server table.

I'm not able to arrive at the solution as status code is part of the composite primary key for the table and
it cannot be null.

Please help me accomplish this as it's extremely urgent.
I need it by tomorrow morning.If I can get the logic/ code , that'll be grreat!

THANKS A MILLION IN ADVANCE