Re: vdpau+mplayer problems
I recently went through this myself. First thing to note is that you can specify these options within mplayer config file, making the codecs list the first "forced" for use but mplayer will fall back to whatever codec it needs if the one required is not in the force list.
Also note the feature set of your NVIDIA chip, I can't get divx acceleration on my GPU. took me a alot of googleing to understand why, check the file link below in my mplayer config.
# Write your default config options here!
# FEATURE SET C (DIVX)
# vc=ffh264vdpau,ffmpeg12vdpau,ffodivxvdpau,ffvc1vdp au,ffwmv3vdpau,
# FEATURE SET A (No DIVX)
Finally I noticed that gmplayer and mplayer don't behave the same when selecting vdpau or not and gmplayer core dumps. I can't be arsed to resolve that though as keyboard controls are good enough for me!