It keeps wanting us to switch to the other document by going to Window
on the menu and selecting the other document.  We want the two windows
to open in seperate instances of Word so we can put them side by side.
One will be a copy we got back from the proofer and the other the
document we need to edit.  We tried the Window>Compare side by side with
  menu option but as we are scrolling down the window, one will
progressively scroll down faster than the other and once they go out of
sync, it's unusable.

Any ideas on how we can get them to open side by side.  This is
happening on Windows XP Pro with Word 2003.

Any help would be greatly appreciated.