No Crossfire option

Hi,

I have a Dell XPS710 which comes with the X1950 Crossfire Edition and
the X1950 Crossfire Series. I've loaded the latest drivers and Catalyst
(8.33, 7.1) yet I don't have a Crossfire option within Catalyst.

I've tried connecting the cable from the VHDCI port on the Edition to a
DVI port on the Series card, and the other end to my monitor, but it
doesn't display anything. Within Displays Manager I have 4 screens - is
this normal? Shouldn't 2 of these be 'merged' if I'm using Crossfire?

I'm running XP Home.

Can anyone suggest what might be wrong here?

Thanks,