Partitionning is not that easy. You have to format ALL your hard disk so it doesn't matter how much space left there is. This is what I recommend to you: find a kind mac user with backup, reformat and partitionning knowledge and ask him to help you to enter this procedure. Of course you could always do some googling to get that knowledge and do it yourself.... If you feel that extra work doesn't worth it, I recommend you to not do it as it seems to be your work machine (work may be more important than hobbying sometimes....)

Bonne chance