The Xsanity guys just published a hint, that using Xsan with Mac OS X 10.4.6 requires to replace a plist file with a file provided by Apple.
The information is based on a knowledge base article by Apple (http://docs.info.apple.com/article.html?artnum=303549) that recommends replacing this file if you work with Xsan 1.1 or earlier.
I haven’t tried this procedure yet (and won’t manage before the end of the month as I am going to attend the NAB in Las Vegas), but the issues described in the articles surely exist with Mac OS X 10.4.6 and Xsan 1.2, so it seems reasonable to follow the steps described by Apple, even if you work with Xsan 1.2.