How to bind two columns as single column in GridView

Question

Hi friends i have one problem please give me the solution for this one urgent

I hava two columns in database those are
validfrom, validto

validfrom        validto
---------  -------
04/07/2011  05/08/2011
05/07/2011  06/08/2011

How can i display these two columns as single column using gridview like this

validperiod
-----------
04/07/2011 -05/08/2011
05/07/2011 - 06/08/2011

Please give the solution for this one please..........i need exactly code for this one.........