Are your PC's Vista_Ready?
We've got some information that will help you decide if your current IT hardware is capable of running Windows Vista here:
https://www.microsoft.com/uk/windowsvista/getready/capable.mspx
In a nutshell, min spec required is:
A modern processor (at least 800MHz1).
512 MB of system memory.
A graphics processor that is DirectX 9 capable.
But to run the fancy stuff like Aero (glass effect and flip-3d etc) and get a "Premium" experience you need:
1 GHz 32-bit (x86) or 64-bit (x64) processor1.
1 GB of system memory.
A graphics processor that runs Windows Aero2.
128 MB of graphics memory.
40 GB of hard drive capacity with 15 GB free space.
DVD-ROM Drive3.
Audio output capability.
Internet access capability.