Yeah the recovery disk would help with that. Also, all you will need to do is put in the live CD. Then when it asks you for a partitioning scheme, you click the, fill empty space or something like that. It will then install Ubuntu on that 50GB space that is left open. Trust me on this, I have built around 15 computers for people and also fixing many and some had to do this with. There is a very very small chance that something will go wrong, if it does, look on the Ubuntu forums, they will help you with everything you need. Also, if you need any direct help just ask me, I am not saying I am a professional on all of this but I have been installing Linux, specifically Ubuntu, a lot. Good luck!