thank you all for the help!
the problem is finally solved.

thanks James!  I realized that the bash is not a login shell when invoked
that way, and my locale variable in .bash_profile did not take effect. the
command line now becomes:

*su -l myname -c '-l' 'startx' *

and worked!

thanks  Sebastian Günther,  this is really a important comment in the man
page that I missed totally, I changed to "-l" instead to avoid the trick


and many nice login manager recommended here, I'll try them out later,
compiling QT or GNOME components is a heavy work for my poor celeron
processor.



thanks again..

fei