SetVariable & Flash player version

I stumpled upon this odd problem. I guess when I make something with Flash MX, then IE and Flash Player version 6 should be enough to view and handle it correctly?

An example:
On a HMTL page where the Flash is loaded, I have a JavaScript function along the lines:

var x = ("_root.clip._x");

Which gives me the x-coordinate of the Movie Clip “clip”. This part works fine in Flash Player 6. However, if I try something along the following:

var x = “100”; ("_root.clip._x", x);

It works fine in Flash Player 7 and the clip moves in the Flash Movie, but nothing happens in version 6.

Did I miss something or is version 7 just required for this?