thekhan's problem is probably that he started the graphical environment as root, then used 'su' to change the user in a terminal. He should be fine if he justs logs in as a normal user from the start.

I have the same problem when I start as a normal user, su to root in an xterm and try to run a graphical program, e.g. ethereal.

PS: It is disturbing to see linux newbies running as root all the time. Please don't do this. It is a dangerous habit.