One OS Per Partition
Before installing Windows XP and an earlier version on the same machine, you must prepare your hard disk with different partitions.
When you install Windows on a new or reformatted hard disk, the Setup program typically does not partition your hard disk automatically. To create multiple partitions, choose Advanced Options during Setup and follow the instructions to create and name multiple partitions. You can also create partitions using Fdisk.
If you have already installed Windows, and you have only one partition, you must reformat and partition your hard drive before you can multiboot.
You can divide your hard disk into multiple partitions, and each partition can function as a separate logical drive. For example, logical drives C: and D: can both exist on the same hard disk, but function as separate disks. You should install each operating system on a different partition. Then install applications on the same partition as the operating system with which you run them. If an application is used with two different operating systems, install copies on both partitions. Placing each operating system in a separate partition ensures that it will not overwrite crucial files used by the other OS.
A basic disk can contain up to four partitions. Each partition can be formatted for use by a file system, such as FAT32 or NTFS.