You can only have one Active Partition active at any given time. When you first setup your hard drive you would have setup a Primary Partition. The Primary Partition is where the (Master Boot Record) MBR is installed. When you select the Operating System to start from that Partition is then marked as Active. Boot.ini acts as a bootloader giving you a choice of Operating Systems. When you originally setup only the first will be a primary partition, the rest will be logical drives within an extended partition, unless you have already setup multiple primary partitions. These can be manipulated with Boot.ini.
You can set up multiple primary partitions, one per operating system. You then have the problem of telling the system at boot time which operating system you want to use. There are programs specifically designed for this task; they are usually called boot managers or boot loaders. What a boot manager does is insert itself into the very beginning of the boot process, sometimes by setting up a special boot manager partition and making itself the active partition. When you boot up the PC, the code in this partition runs. It analyzes the primary partitions on the disk and then presents a menu to you and asks which operating system you want to use. Whichever one you select, it marks as active, and then continues the boot process from there.
If you lose your Primary Partition with access to the bootloader you will not be able to access the other Partitions. You are not gaining anything by having all of your Partitions on the one drive. The best way to do it is to have multiple hard drives. They can be setup the same way by going through boot.ini but if the main hard drive fails it is only a matter of rebuilding the MBR on one of the other drives and reconfiguring boot.ini. This can be achieved by booting to the Recovery Console.
