Hi jumico you should probably have a bit of a read on mandrakes website I am sure that you will find all the info you need.
Anway. You can choose all this stuff when you install mandrake. It will have a partitioning tool as a part of the install.
If all you want to do is wipe everything and install Mandrake and not keep anything it should be very easy.
If you want to dual boot windows and mandrake its a little more complicated. You need to have a seperate partition with windows on it (your first one) then you need to make sure that you know which one it is so you don't install over it.