Windows 7 only: If you've been itching to use the new XP Mode feature in Windows 7, but you aren't too keen on using Virtual PC or just prefer VirtualBox, here's how to use XP Mode in VirtualBox.
We've already covered how to setup and use XP Mode in Windows 7, how to use it on a machine without hardware virtualisation, and then how to create your own XP Mode for any version of Windows with the freeware VMWare Player software, but if VirtualBox is your virtualisation platform of choice, writer Matthew from How-To Geek (my home away from Lifehacker) has you covered with a guide to setting up XP Mode under Windows 7 using VirtualBox instead of Virtual PC.
The basic principle is pretty simple, requiring you to just install XP Mode from Microsoft without the additional Virtual PC component, creating a copy of the XP Mode virtual hard drive, and then using it as an existing hard drive in a new VirtualBox VM. Because you can only legally install XP Mode for Windows 7 Professional or Ultimate PCs, if you're using a different version you should probably create your own XP Mode that works anywhere.
How To Run XP Mode in VirtualBox on Windows 7 [How-To Geek]