Welcome to Seven Forums,
According to this: "WPA2-PSK/WPA-PSK supports WPA1 (and WPA2 but HF doesn't support WPA2)".
You'll have to do a research on what type wireless network adapters(built-in or not) the computers will have and if this will support WPA1, it should work with Windows 7.
Also, WPA1-PSK is not as secured as WPA2 that uses AES encryption, you should inform your client about the security issue. WPA2 Enterprise is even better.