I've tried this IP reservation before, and it does work. IF you never change the network devices. I had my file/print server set this way for quite a while, until I upgraded it and it just refused to give the new mac address the IP after I changed it, so I just set it in the server. It's best to just set a specific IP to the device that is out of the DHCP range.
A couple of questions, why do you want to make all the computers static?
What OS is all this stuff running? You do it different ways on different OS's.