Eight alerts are already written for all four alert categories. These all obey the result from the corresponding message function.
The beep alerts simply sound the terminal bell by calling
ding. They are disabled by default.
The echo alerts display a message in the echo area by calling
message. They are enabled by default.
The switch alerts switch to the buffer where the event occurred
(chat buffer for incoming messages, roster buffer for presence
changes, browse buffer for completed queries). They are disabled by
default. Take care when using them, as they may interrupt your
editing.
The display alerts display but do not select the buffer in
question, using the function display-buffer. See Choosing a Window for Display (GNU Emacs Lisp Reference Manual), for information about customizing its behaviour.
This is enabled by default for info requests.
The wave alerts play a sound file by calling
play-sound-file. No sound files are provided. To use this,
enter the names of the sound files in
jabber-alert-message-wave, jabber-alert-presence-wave
and jabber-alert-info-wave, respectively. You can specify
specific sound files for contacts matching a regexp in the variables
jabber-alert-message-wave-alist and
jabber-alert-presence-wave-alist.
The screen alerts send a message through the Screen terminal
manager (see http://www.gnu.org/software/screen/). They do no
harm if called when you don't use Screen.
The ratpoison alerts send a message through the Ratpoison
window manager (see http://ratpoison.sourceforge.net/). They
do no harm if used when you're not running X, but if you are running X
with another window manager, the ratpoison processes will never exit.
You can look at them with list-processes.
The sawfish alerts send a message through the Sawfish window
manager.
The festival alerts speak the message using the Emacs interface
of the Festival speech synthesis system (see
http://www.cstr.ed.ac.uk/projects/festival/).
Additionally, for one-to-one and MUC messages, there are scroll
alerts (enabled by default), that aim to do the right thing with chat
buffers that are visible but not active. Sometimes you want point to
scroll down, and sometimes not. These functions should do what you
mean; if they don't, it's a bug.
Some of these functions are in the jabber-alert.el file, and the others are in their own files. You can use them as templates or inspiration for your own alerts.