I have this code behind an asp.net button click event

Code:
Response.Write("<script language=""javascript"">" + "window.open('taxcalc.aspx?id=" + matrixID + "&mileage=" + ddlMileage.SelectedValue + "&opts=" + opts.ToString + "','product','toolbar=0,scrollbars=0,location=0,statusbar=0,menubar=0,resizeable=0,width=250,height=500');" + "</script>")
The window opens fine except that the layout of the parent page messes up, it jumps to the left side of the page and a lot of the css doesn't render properly.

Is there a better way of doing it to prevent this happening?

Thanks