Each partition on a hard drive can have a different operating system as long as the Mac hardware will support that OS. Use Disk Utility to format the disk, partition into what you need, use your install DVD to install the operating systems.
If you plan on doing this to your internal hard disk then I would caution against it. Buy a large external hard drive that you know works with a Mac and start from there. Don't do development on a production system.
As always, make sure you have a backup of your production drive, and have tested that you can boot from it, before you start - even if you are going to install on a spare hard drive - because things do go wrong.
If anyone can help, I would really appreciate it.
I'm wondering if it is possible to install different MAC OS versions (for example, having Leopard and Tiger OS X) on the same computer, as you usually do with different versions of Windows just making some partitions.
Is it possible? If yes... how?