If I buy VM ware fusion to run on my mac to I still have to buy windows vista?

Yes, you will have to purchase any operating system (unless it is free) that you wish to use with it, as it is having a brand new computer without the OS, except it is virtual. You will have to put in the OS CD and install it onto the VM. Either VMware or Parallels (maybe both) also have support to boot your BootCamp volume too.