How do you block ANY email from being accessed on computers?

I have a small company with only two computers in it. When ever we leave the room the employees that should be answering phones and doing other work sneak onto the computer for hours on end, then their work gets very far behind. I found how to block MySpace through the internet options / content, but it will not block any email accounts because they are not rated. If I block all addresses then I cannot get to the things that I need without a password for every site that i need. Any suggestions would be greatful. I am trying to make sure that I am paying them for work, not time on the computers.

How do you block ANY email from being accessed on computers?spyware

You could just password protect the screen saver, but if your staff lacks the maturity to do their jobs without supervision they should be replaced.

How do you block ANY email from being accessed on computers?virus scan

You can't really block them, and even if you did, they would find other ways, just as highschool students find ways around their school computer. If they aren't doing their job, then I would give them a warning, that they may not have a job if they continue not to do what they're supposed to be doing.
could you move them to a phone room with no computers in it?

you could also make the log-in to the computer REQUIRE your password to get past the first screen
Have all your email go to a password protected account...as in hotmail or Yahoo.