I've recently been working on a few changes to the Kopete Meanwhile Protocol Plugin, which allows you to use Kopete, the KDE instant messenger client, to connect to Lotus Sametime servers. The update has now been committed to the development branch of Kopete, and should find its way into to the main KDE 3.5 tree soon.
The changes implement some neat new features, such as server-side buddy-list suppport and allowing contact name lookups.
Changes are in KDE svn, revision 491724.