Use the command line.
Open the folder where your movie is and launch mplayer:
mplayer -ao pulse -vo vdpau -vc ffodivxvdpau,ffh264vdpau,ffmpeg12vdpau,ffwmv3vdpau,ffvc1vdpau MOVIENAME
Of course MOVIENAME is the files name. The many vdpau items are there to make sure all encodings are played (h264, divx, wmv, vc1, mpeg1/2).
Basically the idea is the following:
mplayer -vo vdpau -vc *vdpau moviename
You have to explicitly set the vdpau output device to *vdpau with -vo AND -vc to ensure hardware decoding, setting only -vo vdpau will use software decoding to the vdpau output device.
PS. If it works, you should have ~10 % or less CPU usage on 1080p movies...