You can not open a window that is completely invisible to the user; you can use JavaScript to open a window and try to position it off screen but there is no gurantee this will work. (The user will also be able to the window in their Task Bar.)
You could use a 1px X 1px Iframe to load the page but, as peter pointed out, the user still could get at your source.
In any event, this seems somewhat abusive to me, what exactly are you trying to do.
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