With enterprise level equipment, you can indeed lock ports which haven't registered with certain services (or weren't pre-registered.) You can also do what is known as lock-and-learn on some middle class equipment, which basically takes a snapshot of connections to a network device, and then doesn't allow deviation from that snapshot. While that prevents static ip users, it also prevents new DHCP clients. Of course the problem here is that middle and enterprise class equipment cost much more than the standard home/small business equipment.
For a business with 5 users, your best bet to prevent static IP address interference is to use non-standard DHCP pools. Most static IPs from home networks will fall in the 192.168.1.* (or /8, however you prefer it.) Since all of 192.168 is reserved for internal, private use, you could go off and use 192.168.5.* for DHCP. Static IP machines would then only interfere with each other.
Some smaller routers will allow you to lock down to hardware addresses. If you only allow known NIC addresses, the others wouldn't be routed. Once someone says "I can't get on" you can tell them how to configure things, get their address, then unlock. This is a slight variation on the lock and learn theory, save it's not port specific. At the moment, I can't think of a model that would do that for you, I'm sorry...
Also keep in mind Mac's can define different network location profiles. I have one for grandparents house that uses DHCP, one for home that uses DHCP but with set DNS servers (my ISP's DNS sucks), and I have one for a friend's house with a static IP. Switching between them isn't hard to do before you connect, and avoids interfering with other potentially intentional configurations.
Hope that helps.
