when you set a hard disk partition as "active" it simply means which partition it is going to boot up first. if you want to dual boot more than 1 operatng system you have to make a primary partion for each resulting in at least 2 primary partitions. let me elaborate:
you must have at least 1 active primary partition. each hard disk can have a maximum of 4 primary partitions or 3 primary and 1 extended partition. operating systems should be installed on primary partitions only. here is an example:
hard disk 1 on primary IDE channel on controller IDE1:
primary with winxp installed
extended with 3 logical drives E,D,and F
hard disk 2 on slave IDE channel on controller IDE1
Extended with logical drives G,H,I,K,L and M
as you can see at least 1 physical hard disk needs to have a primary partition to install the operating system. a primary partition is not required on all disks only the one with the OS installed. it is up to you what you want to use.