Yes, you are looking for "balloons". I don't use Tkx, as it's special to windows, but google for "perl Tk balloon example" and you will get the idea of how it is done. The Tkx distribution must have a balloon example in it's release, maybe grep thru the example directory, or docs, for the word "balloon".
P.S. I guess Tkx is cross-platform....I'll have to check it out.