You can probably pre-order Windows 7, just like you could with Snow Leopard.
I think VirtualBox is free, so you could download that and try it, but it is shareware / freeware, so it's not as user-firendly to set-up (or as someone said above, not as idiot-proof). VMWare, Parallels, and BootCamp are "proper" products by professional companies.
VirtualBox is as "proper" as the others. VirtualBox is not shareware or freeware, it is an open source project.
And to another poster above, VirtualBox is a virtualization program, just like VMWare and Parallels. In other words, yes you install Windows (or any other OS) on it.