A few weeks back, I had a need to install the latest copy of libxml2 on my Intel Mac Mini here at home. Little did I know what trouble it would cause! First, after installing 2.6.27, I noticed that Colloquy, my IRC client, wasn't so stable. After downgrading to libxml 2.6.16, all of my Office apps stopped working! The icons would bounce once on the dock, then poof...nothing.
So, after tons of Googling, I discovered the Console program. Upon running this and trying to start various Office applications, I noticed an error for libxml2! Now, of course I couldn't find out what version of libxml2 was installed with the latest 10.4.9 update, so I SCP'd over all of /usr/lib/libxml2* from my work MacBook, onto my Mac Mini and poof...everything's working again.