Limiting internet download

Hi,

I run a small office , in which we have wire less connectivity. In all there are some 6 systems sharing the connection.

My problem is my office staffs download things insanly (of course their personal favorites , nothing to do with profession through out the day)

I want to block all downloads , except from my company domain. (email client)

Can somebody please give me a solution where i can bar the systems from downloading any thing from any where , but except from my company domain.

All the systems run on xp. I don't want something where i will have to spend money , perhaps some setting it could be suggested.

Thanks

I'm in the same boat, almost. A systems manager on the road for here has access control to http traffic, but prob is some depts here need full access where as some do not. There are to many computers that need to have limited access put on that are on a proxy we all use. So the question is how to limit access on computers locally without blocking the proxy?