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Your idea is entirely great, replacing CRT into LCD or LED monitor is way effective in saving energy, and for the old one, you can sell or donate them instead to a company that are using anaerobic digester for scrap or waste product. For the energy consumption, you can always turn off every system once they are not being used, unplug them if necessary.
You might want to inventory all your computers and remove whatever expansion cards that you're not using. It's probably not such a big deal with newer pc's running Windows 7, but we found that our older users on XP machines sometimes have modems or soundcards or such attached to their computers that they don't use/need. Eliminating those cards will reduce a pc's power draw.
Our company banned plugging in personal items at your desk that aren't work-related. It's kind of a creepy rule but we had one guy (won't name names) who nearly set his cubicle on fire with a hotplate he used to heat up his soup rather than going to the break room and eating with the rest of us. With this new rule in place, I started looking up ways to reduce power consumption at home and learned that a lot of household devices are drawing power even when not in use - like the dvr, the toaster, etc. There's no way I'm unplugging the coffee pot every day - I'll never remember all that. But I discovered that some companies like Belkin are making new surge suppressors that can monitor or turn off the devices that are plugged into them. This might be an option for your office, even though it wasn't for mine.
One of the biggest sources of heat (which must be cooled) and noise in pc's is the power supply (PSU). Traditionally, when modders talk about hot-rodding their systems, they emphasize the case design or the flashy fast/new parts that use lots of power. However, there's a growing movement towards making "silent pc's" which is also dovetailing quite nicely with our shared concerns regarding energy reduction and saving the environment. Perhaps the PSU is overlooked by most people except for gamers, who want / need more power. But the green/quiet movements are inspiring fanless, energy-efficient power supplies for desktop computers. I recommend checking out the Corsair VX450W. Now it costs $80 or so online, so if you were planning to outfit an entire office that will cost a bunch of money up front. But you'll get that money back over the course of the 3-5 years that your office keeps your computers running. And as an added bonus, your pc's will run quieter as well.