How to Avoid create new Window when Click Querystring ?..

                 I would need a requirement that , i had one that will create a new window and it had its details using the query string variable.

The thing is , that is working fine.but  i need as follows,

               when i try to click the link , i will create new window and its corresponding details using querystring, so one window was already opened 

at the same time , if try to click another link from the grid again new window created with its deatils.  i don't want to furthermore window ,it should reloaded 

on the same window.

            For avoiding multiple window created   in tandem ...

Thank in advance ,

- Karthik