virtualbox.org

I need to buy a Windows 7 so I can test web sites in IE9 and 10 on my Mac using Vbox.

Seems like I get to choose either 32 or 64 bit versions of Windows. Can anyone help me choose?

Pop in the install disc and if it gives an error, you know you need the other one. It's clearly written on the disc what edition you have. Either will work with the right hardware and settings.