You probably know that you have to buy any virtual machine operating system separately from buying Paralells Desktop.
I bought Windows XP online, got a physical Windows XP CD with genuine serial number in the mail, created from this CD on my older iMac (with DVD drive) with Disk Utility the ISO image, copied that image file onto a USB stick and from there onto the other, newer iMac (without DVD drive). I then installed Windows XP from this ISO file from within Parallels Desktop as a new virtual machine.
If your Mac has a DVD drive you can install Windows XP, of course, also from within Parallels Desktop directly from the Windows XP CD.
Last edited: Aug 20, 2013