Mike,
Based on what you are looking to do, and the constraints that you have, I will suggest an alternative that we came up with for practices that wanted less headaches/IT work but for a variety of reasons were not able to take advantage of our managed environment.
Invest in one machine of modest performance, install a third-party terminal server solution, and run AC on that machine with the other machines running sessions on that one 'server'.
The second part of this is accessing the server from 'ChromeBooks', cutting your hardware cost by 100-300%. ChromeBooks are ~$250 and require almost no maintenance.
The third part we recommend (but is optional) is making the host OS for the 'server' CentOS (or RedHat if you want commercial support). This gives you a bullet-proof host OS that costs you nothing, high performance virtualization, and the ability to easily image your server regularly. As an added bonus, you can copy the VM, do a AC upgrade, and determine if you like what you get - all without disturbing your existing production system. As Wendell says, "Did I mention that it is FREE?"
This allows you to mix-match other machines, as all they need is a browser.
Of course, you can save yourself time and money by switching to existing old machines to consumer Linux like Fedora or Ubuntu, but that requires a little more expertise.
It is your network, but the industry standard is to NOT allow users to have administrator privileges - that is THE way machines are compromised. In the SMB/Enterprise world once a
machine is compromised, the hard drive is wiped and a fresh install from image is restored - it just takes way too much time to clear a machine, not to mention lingering after-effects and questions.
