how to get the selected dropdown item as the filename in the savefiledialogue box

Question

Hi,
I am Using the Dropdown which is having the table name populated from the database.based on the dropdown value datagrid will be populated in the same page and i am using the Export option and it will export the whole datagrid,now I want to display the dropdown selected item as a file name in the savedialogue box,

I am Using silverlight 4.

Reply with the solution would be really apprecaible.

Thanks and Regards
Ragavendran.S