Process.Start(iexplore.exe) running from asp.net c# code

hi,
I have a web form that takes user credentials and checks against Active Direcotry and it works fine. What is required is to open new IE under this user's security context (who has just entered his credentials). In code behind of login button click event i have

ProcessStartInfo pInfo = new ProcessStartInfo();
pInfo.FileName = @"C:\Program Files\Internet Explorer\iexplore.exe";
pInfo.Arguments = "http://www.intel.com"; // also tried with -nomerge
pInfo.UserName = username;
pInfo.Password = secPassword;
pInfo.Domain = domain;
pInfo.UseShellExecute = false;
Process.Start(pInfo);

this code should open new browser under user credentials of the one who has entered his credentials on web form not the one who is already logged on to the operating system.

its like "runas" option that we get by righ clicking on IE icon.

When i run same code in Windows forms it works fine but not with asp.net - I think only one instance can be executed of Internet Explorer at one time programmatically.

i have been googling this all day and finally thought to ask you guys if anyone here knows the reason for this behaviour

any help will be great - thanks in advance