Dynamically making a field mandatory.

Hi All,

I have 2 radio buttons , say A and B . And 1 Field say FIELD1 which is disabled by deafult.

Now if I select Radio button A , Field1 Should become mandatory

Whereas If I select radio button B then  - field A should be  disabled again

Now if I declare field 1 as mandatory, the problem is that if the user selects A, which Enables Field 1 and then

he changes his mind and wants to select radio button B instead. He gets an error since Field 1 has become

enabled and mandatory...

How do we handle this problem. Please help

Regards,

Faiz