I think it would be a fantastic addition to openfire/spark if you integrated some kind of desktop viewing/sharing into the spark instant messenger. That would make your software complete. At least from my viewpoint....
try out the Red5 plugin in the beta plugin section. It has a remote viewing window ability, also you get a pretty decent video conference solution (more 1 to 1), that has video messenging and video roster.
Anyhow the desktop sharing is java based included in the Red5 plugin. Give it a shot
Hope this helps