As a su, emacs can't be displayed..

hello, As a newbie, I faced with a kind of simple problem... In a su mode, i want to open some file with emacs so I typed 'emacs ...' as usual. Then, I got the following message, emacs: Cannot connect to X server :0.0 Check the DISPLAY environment variable or use '-d'. Also use the 'xhost' program to verify that is is set to permit connections form your machine. What should I to fix this problem? Thanks, CK, _________________________________________________________________ Say “goodbye” to busy signals and slow downloads with a high-speed Internet connection! Prices start at less than $1 a day average. https://broadband.msn.com (Prices may vary by service area.)