Table Validation: How to prevent name from appearing more then once

[Jarekb]

I'm about to start building an xml form with a table where the user enters a name and number of hours worked. The name field will be a drop down box with all authorized names. How do I prevent the user from entering the same user multiple times in the table?

On a side note, how do I retrieve and send data to a specific cell within a table?

Thanks