The rules for partitions are as follows:
You can have up to 4 primary partitions on any drive, or you can have up to 3 primary partitions and 1 extended partition. Within that extended partition you can have essentially infinite numbers of logical partitions, until you run out of space.
So you can think of it like an office building. You have three managers who all have actual offices, and then a big open area with a bunch of cubicles. You can arrange those cubicles in any way you want, but you're limited to however large the floor is.
Am I going mad- the seagate 320 gb sata hdd can ONLY put 4 new particians, with paragon! Ive always been under the impression that any number could be created (and the normal settings etc) but Im left with a ton of free room(unassigned and unformatted) at the end!? Surely not- the continuation of partician creation is not given after the fourth, paragon partician manager swtched off availablity, there are no messages or reasons?