If you are like me, you have quite a few 3rd party System Preferences panes installed. In 10.6, if any of them are 32-bit panels (in my case, that's most of them), then you need to re-launch System Preferences in 32-bit mode to load them. I was getting bored of this and discovered a very simple workaround.
Select System Preferences in the Finder, select File » Get Info (Command-I), and tick the 'Open in 32-bit mode' checkbox. Job done.
I have not seen any problems using the Apple-provided panes in 32-bit mode. This simple trick will help any applications which are not fully 64-bit, particularly people who have a 64-bit app with 32-bit plug-ins, as described in this hint.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090831003645829