Javascript: window.open ...

Wow haven't posted here in a while.

Anyway, here's the trouble:

I'm currently using this code to open a new window:
window.open("admin_show_preview.php","preview_window","toolbar=yes, location=yes, directories=no, status=no, menubar=yes, scrollbars=yes, resizable=no, copyhistory=yes, width=760, height=500").focus();

Now, whe the button that uses that code is clicked, if the window is not already open, it should open it, however if it's already opened it should refresh. Now i found that by using that code by itself in the button, it refreshes that popup window, but not from the server. The result being that it becomes worthless.

Does anyone know a way to get window.open to always get the page from the server? Or even a better way to get the result i'm looking for?

Thanks,

Dan.