It is allowed to install Windows 7 in other PCs in the same disk as long as it is beta version or evaluation copy. If it isn't, your other PCs which has Windows Seven installed will be blocked when you are connecting to internet.
The retail version will allow you to install the OS on multiple computers. An OEM version of Windows 7 will only work with one computer at a time or will blocked after connecting to internet.
Windows 7 Evaluation Copy is same best as completed Windows 7. You can update them for free.