If you had previous versions of QuarkXPress installed, you could painfully save backwards. My memory (very dim now!) is that you could only save back to the previous version. If that is true, you could save QX 7 > QX6, then QX6 > QX5, then QX5 > QX4.
Quark (as far as I know) has had nothing similar to IDML for saving backwards.
Just wanted to be sure before going after the Q2ID plugin. Thanks