Restricting Internet Access

I have a client that needs to allow her employees Internet access to be able to order parts and lookup information from a specific website. But she does not want them to have open access to the Internt due to proir abusive surfing practices. Is there a software product or a way to setup the net that would limit access only to sites she has approved? Her ISP is AOL, and she has a very small operation (3 employees), so price is very much a consideration. The solution would need to block access byboth AOL and Internet Explorer. Any suggestions?