maximum number of records in a value

[vaughan]

Hi

How I can do to limit the number of times a value is selected in a dropdown? I mean, I have a dropdown with 4 element values ??for a registration form for an event:
value1: limit of times you can choose 20
value2: limit of times you can choose 100
Value 3: limit of times you can choose unlimited

When the entries are finished, you see "closed" or simply can not choose or error messages ...

Thanks

Regards