I wrote an article about home automation with XTension and Indigo for Macworld magazine a few weeks ago. It's out now, in the September 2005 issue, starting on page 64. It's part of the "Old Mac, New Tricks" feature; which includes other nifty things you can do with a spare Macintosh. I hope that you enjoy it.
Here are clickable links to the products mentioned in the article: