How do you send a pop-up message to a LINUX KDE or GNOME user?

excerpt from  man wall :
NAME
       wall -- send a message to everybody's terminal.
SYNOPSIS
       wall [-n] [ message ]
DESCRIPTION
       Wall  sends a message to everybody logged in with their mesg(1) permis‐
       sion set to yes.  The message can be given as an argument to  wall,  or
       it can be sent to wall's standard input.  When using the standard input
       from a terminal, the message should be  terminated  with  the  EOF  key
       (usually Control-D).
       The length of the message is limited to 20 lines.  For every invocation
       of wall a  notification  will  be  written  to  syslog,  with  facility
       LOG_USER and level LOG_INFO.
OPTIONS
       -n     Suppresses  the  normal  banner  printed by wall, changing it to
              "Remote broadcast message".  This option is only  available  for
              root   if  wall  is  installed  set-group-id,  and  is  used  by
              rpc.walld(8).
ENVIRONMENT
       Wall ignores the TZ variable - the time printed in the banner is  based
       on the system's local time.

other option is to install talk-client and talk-server
Talk client for one-on-one Internet chatting
The talk package provides client and daemon programs for the Internet
 talk protocol, which allows you to chat with other users on different
 systems.  Talk is a communication program which copies lines from one
 terminal to the terminal of another user.
 
 Install talk if you'd like to use talk for chatting with users on
 different systems.

The wall command works well for console users but it doesn't seem to do anything on the kde screen of the linux computer when I attempt it. Talk is the same thing - a console chat (unless there is something I am not aware of).

"but it doesn't seem to do anything on the kde screen of the linux computer when I attempt it"
Strange , because once I type  wall "my message"
Kwrited pops up telling it is listenning on Device /dev/pts/0 ( ine window tile) and with
"my message" displayed in the pop-up window.

I'm using PCLinuxOS Test 2 but I know it works on SUSE 10.2 without any problems.

What happens when you change to /usr/bin  directory where wall executable is located?

kwrited is supposed to allow the user to receive write,talk and ytalk messages from ttys or from other users logged in in X sessions.
http://www.archivesat.com/For_developers_of_Konsole/thread636771.htm
http://enterprise.linux.com/comments.pl?sid=34687&cid=83931

I see what's  happening now.  You are correct, it does work properly when using the command:

$ wall -d "My Message Text"

and DOES pop up on the KDE clients.  It didn't pop-up on the GNOME client because kwrited is not in the GNOME configuration.