mplayer gui can't open dvd or vcd

[Yuandan Zhang <yzhang4 turing une edu au>]

hi,

I installed mplayer and mplayer-gui 

mplayerplug-in-2.80-0.lvn.1.4
mplayer-1.0-0.lvn.0.26.pre7try2.4
mplayer-docs-1.0-0.16.pre7.2.fc4
mplayer-mencoder-1.0-0.lvn.0.26.pre7try2.4
mplayer-fonts-1.1-3.fc
mplayer-gui-1.0-0.lvn.0.26.pre7try2.4

i can player dvd or vcd by 

mplayer dvd://1 or mplayer vcd://1 

however, if I tried to open DVD or VCD at mplayer-gui (gmplayer), I
always get error alike:

Error opening/initializing the selected video_out (-vo) device

How to fix it??

thanks

Yuandan