Apple has posted Java For Mac OS X Update 1 version 1.0 which includes Java SE 6 version 1.6.0_05.

This Java for Mac OS X 10.5 Update 1 adds Java SE 6 version 1.6.0_05 to your Mac. This update does not replace the existing installation of J2SE 5.0 or change the default version of Java.

For more details on this update, please visit this website: http://docs.info.apple.com/article.html?artnum=307403

The update weights 57.5MB and is available either through the Software Update utility or on Apple's web site