On MS's site, you can download VMs for use with an existing Virtualization Platform like Parallels or Virtual Box. The VMs are guest operating systems with limited trial time. MS's docs suggest you use your VM manager to roll back when time runs out.
With the USB key promo, you get a full license for parallels and a full license for Win8.
With the USB key promo, you get a full license for parallels and a full license for Win8.