Web program to share documents

I manage a small business with about 40 employees.  I would like a simple system by which to share documents that can be accessed via the internet from home for them.  There should be documents that everyone can see and then documents that are protected from anyone but them.  This seems to be a more simply way of having all the right forms, administrative paperwork, etc that people need on a regular basis.

We have a website that we host through hostgator.com and use windows 2003 server if any of these things would prove useful.  I would prefer to purchase software that did this for us instead of a fee based monthly service.  

Thanks for the help!
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