After studying how to install Yosemite from this website, I was able to create a bootable installation cd and finally install it in a separated partition.
So I can use Windows 7 and Yosemite ate the same laptop now.
However Yosemite isn´t going throught because it´s stuck in the initial screen saying ''keyboard not recognized'' and it also keeps asking for a wireless keyboard.
Apparently the OS isn´t recognizing the keyboard of the laptop. How should I proceed?