1) No, install mandrake linux and dual boot, you should be fine.
2)You will need a separate partition and you dont need partition magic> During install, linux will ask you if you want to install it on a separate partition..click yes and it will do it automatically for you.
3) You can get it back..there are a lot of people willing to help here. + You will still have windows on other partition in case of emergency.
4) Mandrake 9.1 or Redhat 9.0