[UPDATE]Since Nvidia driver version 180.35 almost all Nvidia graphics cards starting with the 8xxx series are able to play back VC-1 content.[/UPDATE]
VC-1 is one of three open standards for HD DVD and more important these days, the Blu-Ray disk.

If you’ve already bought a graphics cards, and you are not certain if your card support VC-1 with Nvidias new VDPAU driver, you’ve got two possibilities to find out if your card does support VC-1 natively.
Install nvclock:

apt-get install nvclock

and look for G98 or G96:

nvclock -i | grep Archit -2

In this case, I’ve got an G98, because I do have an 8400GT, a 9300GT would result in G96:

-- General info --
Card:           nVidia Geforce 8400GS
Architecture:   G98 A2
PCI id:         0x6e4
GPU clock:      612.000 MHz

Or you can check it out with this little tool, which tells you a bit more about other features, too: http://www.cs.rug.nl/~wladimir/vdpinfo/

Download the latest version, and perform a simply a make in the vdpinfo directory.
Or use my binaries compiled on a Ubuntu 8.10 here x86 version 0.5 and x86_64 version 0.5: (NO WARRANTY!)
You’ll also need the latest Nvidia VDPAU driver. Currently it’s version 180.27. The easiest way to install it, is to use a repository from launchpad PPA. (Debian and Ubuntun only). This is what I’ve added to my /etc/apt/sources.list:

# nvidia experimental driver
deb http://ppa.launchpad.net/anders-kaseorg/ubuntu intrepid main

afterwards I’ve performed a

apt-get update
apt-get install nvidia-180-kernel-source nvidia-180-libvdpau nvidia-180-libvdpau-dev nvidia-glx-180 nvidia-glx-180-dev

Now restart KDE or Gnome (Ctrl+Alt+Backspace).

You will also need to perform this command in a X environment. E.g. it doesn’t work in a ssh session.