For those not familiar with the PCI/VGA pass-through support for Xen virtualization, watch this demo made by Ubisoft and the description within that article. The game development studio was playing around with Linux and Xen virtualization whereby they passed a graphics card to their DomU for gaming. That's a video from last year and still fairly interesting.
This week on the Xen mailing list was a report of a user passing his NVIDIA GeForce graphics card to a Microsoft Windows 8 Consumer Preview HVM DomU and Windows XP Home Edition SP3 HVM DomU from his Ubuntu 11.10 system ruunning an Intel Pentium CPU and the Xen stack was from Xen 4.2-unstable.
The Xen user, Teo En Ming, has written a 13-page PDF guide about how he setup the Xen VGA pass-through support for those looking to play around with this feature. Here's the PDF guide. "If you want to follow all the steps in the PDF file documentation which I have written, I can guarantee you great success to Xen VGA Passthrough with Windows 8 Consumer Preview HVM domU."
Additional information on the Xen VGA pass-through support is available from the Xen Wiki.