I updated to OS 10.5.6 yesterday. After the update, I found that when attempting to install refit, the installer blocks clicking on the next/install button. This is also true of another product which accesses OS X resources called onyX. I hope that this is just a minor irritant and it can be worked out. My thought is it is purely coded into Apples code to block these apps from performing installations.
Note: As I good give a poo about reinstalling, I will give it a shot and not update in order to prove my point and case. Luckily after updating, I can still use alt/option key at boot time and the Ubuntu partition is seen as Windows.