Ahh yes, the TCO mantra. TCO is a means and not a goal. So Apple is more cost effective (cheaper is such a nasty word, dont you think) than Windows. Because you seem so knowledgeable could you please do the calculation for me?
120 Windows XP SP2 workstations, all generic Dells. Standardised image containing a client for use with a core system that consist of two Mimix mirrored IBM iSeries i520 midframes. MS Office 2003, Citrix client, Adobe Reader and Lotus Notes client. Take PC from box, plug into network and start RIS. RIS is followed by unattended app installation. PC is up and running within 20 minutes. No user files are saved locally. Policies cater for what a user may or may not do. AD caters for the rest. Back-office consist of three HP servers running VMware ESX 3.x. All Windows servers (10) are thus virtual and that ESX cluster provides us with load balancing on server level and non-stop redundancy. Network storage is by two mirrored EqualLogic boxes.
We run a 24/7 business where time is money. I know what a PC including all programs and service (do we need service?) and personnel costs on a yearly basis. We use a particular flavour of Windows and the office suite for at least 4 years. I even know what it cost to build the images.
So, do the math and gimme above setup in Apple terms of $$$$ You may even use the Mac Mini! And most important: explain the added value of using 120 Macs in such an environment. And one more thing, because of our highly standardised and straightforward IT landscape we can do with very few staff.
Unix? Meh...