I find the demos included in the tarball invaluable.
When beginning with complex systems, it easier to adapt some existing codes than to roll-up ones own from scratch.
Usually (and depending on you installation system, perl pecific or not: ppm,
cpan, rpm, apt-get...), these demos are not included in the installed system.
Also Advanced Perl Programming contains some material
about Tk. It is one of my three favorite perl books
with the bible
Random hints: even if Tk is quite oldish in its look, it
has two powerful widgets: see Tk::Text and Tk::Canvas, also
the power of GUIs is in the ability to define new event
handlers: see Tk::bind.
stefp -- check out TeXmacs