How can i use Response.write not to cause a screen flash when click on "OK" ?

Hi

I have a message that is build from the server side and writes as follows

Response.write ("<script> alert('Permission is required to view the object')</script>) 

This causes the whole screen to flash when the user clicks ok.. How can i just send the alert message to the client side (maybe through callbacks) and when the user cliks ok the popup alert just closes .

thanks