Once again i will have to bill your company for removing viruses/spyware/some-other-ware from one of your workers' machines. The job took me seven hours of which i only have the heart to bill you for four. After all, i want to keep you as a client in the future too. But for the price i should be billing you, you could get your employee a new computer.
Here's what you should do.
In short terms, educate your users that their workstations are for work only. That it will cost you the equivalent of one new computer each time i have to make it work again after the fun software they installed onto it brings it to a screeching halt. this money could be put into much more fun and/or productive use. Ask them to be very, very careful with the tool you've provided them with. A craftsman will take care of his or her tools even if they belong to their company and not themselves.
Ask them to get a personal computer for personal work. If you can, sponsor them into getting a personal computer. We can even work out something that is so easy to re-install that if it's broken again, it will be painless to get it back to wor... to play.
Or we could put all the work stuff on a terminal server. The users can bang their computers to bits for all i care, but the work is behind a remote connection.
Here's my favorite one, and it's not even expensive. We'll install a second environment for your people to play with. If they're at work, they boot into "work mode" and if they're at home, they boot into "play mode". I have the perfect suggestion for you.
So please, let's sit down and talk. This will only take a while and you'll save lots of extra money for it.
(fictional message to a customer)