can't play avi files. shared library errors with lots of applications.

firstly, thank you to the people on this forum, you are all really helpful.
this is my first mac, and i'm having problems running programs. i'm trying to play avi files in quicktime, but it's not working. i have downloaded 3ivx which then suggested i download DivX Doctor II 2.2, which i did, and when i tried to install it, it told me:
The application "DivX Doctor II" could not be launched because of a shared library error: "<DivX Doctor II><DivX Doctor II><CarbonLib>"
i'm also having the same error message when i try and install microsoft office for my mac. i don't know what to do, being a first time mac user. i have run repair disk permissions but this hasn't seemed to change anything.
what can i do to run these programs and install microsoft office too?
thanks in advance.