I have discovered a way to publish multiple simultaneous slideshows from one .Mac account. The tutorial is posted at here on the www.dotmac.info site. Linked from that tutorial is a Preference Pane I have written to enable users to subscribe to these previously hidden slideshows.
[Editor's note: I have not tested the hint nor the referenced Pref Pane.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20021103060848473