OS hardening

It depends on what you mean by OS hardening.

Do you mean
A) to lock down the PC so that users can not alter the workstation setup, or
B)do you mean secure the workstations from malicious attacks.

If A, then if the workstations are in a Active Directory domain you can use Group Policies to lock down their configuration, and limit what users are able to do.

if B) then grab then get yourself a copy of Ghost (or similar copying product), grab the CIS security benchmark for your operating system from http://www.cisecurity.org/, prepare a single machine to a Standard Operating Environment you are satisfied with and use ghost to replicate this across the other 19 workstations.

Hope this helps.

Using the Security Templates you can apply restrictions using the Local Security Policy to lockdown the workstation. Basically apply a predefined security policy to your workstation.

Of course, you can use Group Policy (if in a domain) to lockdown workstations instead.