in reply to
Making an application dockable
The Gtk-Perl package has bindings for libgnomeui, which includes applet-widget support. Install the gtk-perl package and type 'man Gnome::reference' to get the raw syntax doc.
What this boils down to - you can write true panel applets with Perl. =)
Here is an example of a Perl panel applet in Gnome (though I hope you don't follow those examples of indirect method invocation ;).
Over at ORA you'll find a short, and not very in-depth tutorial.
If you're equally C savy (and here's where the *good* docs are ;), you'll find the panel API reference quite useful; as well the panel applet tutorial.
But... I must warn you, GNOME 2.0 is under rapid development right now. The gnome folks (and even myself, for some parts ;) are working feverishly to get the bugs squashed. The new versions of GNOME, GTK+, GDK, and GLib provide a significantly changed API, deprecating a great number of things in the old. So those docs above are likely to be severely outdated in a few months when many people are running the new GNOME.
Anyhow, "proper" panel applets are done a bit differently now, relying more heavily on CORBA.
So.. in my reccomendation, if the GUI portion of your code is relatively simple, or small.. It should be rather trivial to port it when the time arises. If, however, you have a *lot* of pop up property dialogs, and extensive graphic manipulations... check out the appropriate modules from cvs.gnome.org first and get a feel for the changes.
Best of luck.. and trust me, Gnome development rocks! ;) Have fun.
Update: Btw, if you have any specific questions or issues, don't hesitate to email me, firstname.lastname@example.org, as I've worked quite a bit with Gnome applets in Perl and C. There's also a quite responsive gtk-perl list (linked to from the gtk-perl page).