File download not working from modal window

gantait

Hi,
In my application i am using modal dialog by window.showModalDialog ()
and from the modal dialog i want to dowload a file by giving file url in window.open()..
my problem is file download promt is comming but with out the file reference , This is due to modal dialog, but i have to use modal dialog and i can't change it.
mozilla and prism browser i am using for my application.
Is there any solution to make it work , file downloading from a modal window..any tricks / any other way..
please help...
thaks in advance