You want to use Response.Reidrect and specify the target frame/window. I googled "asp.net response target", and this was one of the more than 4.6 MILLION results returned:
public static class ResponseHelper
{
public static void Redirect(this HttpResponse response, string url, string target, string windowFeatures)
{
if ((String.IsNullOrEmpty(target) || target.Equals("_self", StringComparison.OrdinalIgnoreCase)) && String.IsNullOrEmpty(windowFeatures))
{
response.Redirect(url);
}
else
{
Page page = (Page)HttpContext.Current.Handler;
if (page == null)
{
throw new InvalidOperationException("Cannot redirect to new window outside Page context.");
}
url = page.ResolveClientUrl(url);
string script;
if (!String.IsNullOrEmpty(windowFeatures))
{
script = @"window.open(""{0}"", ""{1}"", ""{2}"");";
}
else
{
script = @"window.open(""{0}"", ""{1}"");";
}
script = String.Format(script, url, target, windowFeatures);
ScriptManager.RegisterStartupScript(page, typeof(Page), "Redirect", script, true);
}
}
}
With this you get nice override on the actual Response object
Response.Redirect(redirectURL, "_blank", "menubar=0,scrollbars=1,width=780,height=900,top=10");
Google reveals all.