I think its 3. Just to know if I am correct.
/
/boot
swap
I have ubuntu 7 at home on one partition. This is not optimal but serves fine for what it does. We have RHEL4 boxes here at work each one with multiple partitions.
How you configure it depends on what it is intended for. Or did I not get what you want to know? I am taking 'partitions' to mean number of separate file systems on separate logical devices.
I am not sure if the answer is 1 or 0, as I know you can use the entire volume of a disk without using any partitions, however I am not sure if this would be bootable.
/boot and / do not have to be separate partitions.
swap is not necessary, and you can easily create swap space on a live mounted partition as a file.