Here is my educational client, built with PWC and jsjac. It does not have presence changing feature, it just shows how a jabber client could be done. Feel free to use it.
(Was done in a few hours, probably would be good for a quick workshop:)
JsJabber client homepage
(You can test it in Firefox with a Jo-hely (good places) account, registration is free (Hey, my team built it ;)
For those for whom it does not work, a screenshot: