Upgrade Window XP (or 7) to Windows 8 in Parallels Desktop 9

hi all,
I need to virtualize Windows 8, but.... I've Bought Windows 8 Upgrade (), so I need to install a previous release of Windows in order to Upgrade it with Windows 8, now as I remember I've at home two previous release of Windows: XP and Seven.
Some questions:
1) can I install XP or Seven in my virtual machine and Uprade it to Windows 8? If yes, I've to take care about something regarding the VM?
2) Is better starting from XP or Seven?
Thank's in advance,
Fabio