You may need to delete your ~/.mplayer directory (Back it up first, of course, just in case)
When I fist installed mplayer with VDPAU support, the settings would cause mplayer to segfault.
Also, you may want to consider making a new .mplayer directory with a config file, with the following in it:
(That trailing comma on the vc= line is important, it is permission for mplayer to skip on to other codecs should the vdpau codecs not be appropriate for the file you're asking it to play.)
vo=vdpau # Force VDPAU out
vc=ffmpeg12vdpau,ffwmv3vdpau,ffvc1vdpau,ffh264vdpau, #Prioritize VDPAU codecs
framedrop=1 #Allow frame discards