I recently purchased a new macbook pro, this resulted in an 'old' macbook hanging around my desk without being used for some time. As my girlfriend is still working on a old laptop I purchased a couple of years back she was interested in using my old macbook. One of the things however she did not like was the default operating system on my macbook. She wanted to run Linux on it.
Installation of ubuntu on a macbook is very very simple, just take the normal steps of installing ubuntu. however the wifi drivers is a story on its self. If you are installing Ubuntu on a macbook.... don't do what i did, just follow the guide of installing ath9k driver and you will be ready to go. It is part of a ubuntu howto on installing on a macbook.
You can install the ath9k drivers, you can also make wifi on a macbook with ubuntu working with madwifi or a ndiswrapper. it is all in the guide so just follow the guide and you will be able to run ubuntu on a macbook.