I wanted to test VA API with my Lenovo T400s (GMA4500HD aka G45). You first need to install libva and then a libva-enabled mplayer. The only problem I have encountered is that the Debian package in the libva I downloaded disabled the i965 driver. I have reenabled it, it seems working. After installing, I found a small problem, reported on the Phoronix and the hkepc forums both: the skin of the people become blue. This can also be fixed easily.
sudo su
cd /usr/local/src
wget http://www.splitted-desktop.com/~gbeauchesne/mplayer-vaapi/mplayer-vaapi...
apt-get build-dep mplayer
wget http://www.splitted-desktop.com/~gbeauchesne/libva/libva-latest.tar.gz
tar xzf libva-latest.tar.gz
cd libva-0*
echo debian/tmp/usr/lib/va/drivers/i965_drv_video.so >> debian/libva-dev.install
sed -i s/disable-i965-driver/enable-i965-driver/ debian/rules
dpkg-buildpackage
cd ..
rm libva*dbg*deb
dpkg -i libva*deb
tar xjf mplayer-vaapi-latest.tar.bz2
cd mplayer-vaapi-*
./checkout-patch-build.sh
exit
/usr/local/src/mplayer-vaapi-*/mplayer-vaapi/mplayer -vf rgb2bgr=swap,scale -vo vaapi -va vaapi whatever_hd.mkv