Is it possible to use the PCI passthrough facility in ESXI 4.0 to connect a graphics card to a virtual machine? If so, is it also possible to pass through a USB keyboard and mouse to control the VM without using the vSphere client?
I haven't tried this myself, but I've read alot about people who have, as it would be a nice way to "outsource" the HTPC-role to the server.
It is possible (but not supported) with certain setups. It seems Radeon cards and Windows are the most forgiving. There should be no problem with passthrough of a USB-keyboard and mouse, however you will probably have to passthrough the entire USB-controller. The setups are highly driver- and hardware dependent (need VT-d support).
Here is a good thread on the subject (including some success stories): http://communities.vmware.com/message/1754453
I'm sure there are more threads on the subjects since last I checked.
For USB passthrough (or passthrough in general) here is a decent guide: http://tinkertry.com/usb3passthru/
As a sidenote, here's some success stories for Xen: http://hardforum.com/showthread.php?t=1668281