In terms of a general security policy ensure good general behaviour by:
It is important to consult with people over the security policy and explain why it is so important. After all it is everybody’s jobs and reputations on the line if someone transgresses. You will also need to make sure that all of your employment contracts refer back to the security policy so that you have recourse if someone flouts the policy. It is also an idea to periodically check the policy to make sure it is keeping up with the latest innovations and technologies.
The cost of monitoring tools and software vary from £25 - £100 per PC. Setup is very straight forward and is often a download from a vendor's site, taking about 20 minutes to install and configure.
Here are a number of providers of internet and email usage monitoring software:
Creating IT security policies
Business IT Guide
enables businesses to make the right IT decisions