Is it possible if i use server.transfer for po pout windows?? 

Server.Transfer is usually used to redirect the user to a different page. To open a popup you would need to define the appropriate javascript in your aspx page. Is that what you mean?

 that's what i meant..and at the same time i have to pass values from the existing page to the pop out window.

In that case you will need to pass the values by using a querystring.