Windows XP or Vista or 7?

How many computers?

Single or multiple servers? Is the server Windows as well?

What kind of security is lacking. Are you planning to block e.g. peer-to-peer applications, youtube, Google etc.

Without knowing a lot more about your setup, all people can do is guess.

I still have trouble with why you would even ask here. Wouldn't it be better on an IT-security/networking site?