Windows/Linux/Mac GUI?

Hi all,

I am going to start a hobby project, which would be small-scale for
most of you (program that edits text files, following rules in
editable config files, adding user-made content to the existing maps)
but which will probably take most of my summer. As the game works in
Windows, Linux, Mac OS X and Solaris, I would like to support as many
of those OSs as possible.

If I write the GUI using Swing, will the program work on Windows,
Linux and Mac? I don't know what Solaris is or if it has Swing, but
that would be a bonus.

What else should I know about cross-platform developing? What I should
and shouldn't use? I am mostly worried about GUI, but other hints are
welcome and probably needed as well.

Janne Joensuu,
Endoperez
.