[xmonad] VMWare dual head?

Hi, Recent releases of VMWare Workstation can be switched into a fullscreen dual-head mode allowing the guest OS to make use of two physical monitors. Unfortunately this doesn't appear to work correctly under xmonad ... it looks as tho' VMWare is seeing and trying to claim the second screen but is being forced back onto one. This is on Fedora 10 using the the proprietary NVidia drivers configured for Twinview ... VMWare dual-head mode works fine in this setup with Metacity. Has anyone else seen this? Any ideas on how to diagnose and fix it? Cheers, Miles