[CentOS] display pop up message on X

Is there a method to display pop up messages on X display?

I found xmessage, however I was hoping for something a little more
flexible. like being able to tell xmessage to display a file (typically 
one line in the file).
then send it a signal to tell it to re-read the file and show the new data.

Sure I can kill it and re-show it but that isnt very nice...

Is there something available in centos 5 for this that I dont know about?

Thanks

Jerry