I also have a Quad core, Q9300, 4GB DDR3, XP Pro 64 -  and my Vue 7 Infinite shows "4CPU".

Does this always happen (with all scenes at all times)? Some cores might not be used at some times (but not sure of this).

I just did a quick Google search and didn't see anything about this.
If it were my system, I'd start a ticket with e-on support. It doesn't seem to be a Windows issue.