You can very well have multiple primpary partitions on your hard disk. The problem is with Windows - it should be able to "see" only one primary partition. If you create partitions with Disk-Id different than FAT/FAT32 (e.g. partitions of type Linux or Linux-Swap), they are "invisible" to Windows, and the OS is comfortable with them. The problem comes when you try to create two primary partitions with FAT32 type, and one of them happens to be your Windows boot drive.
Manish
<i>I have started to be irregular with this site now...</i>