From the Linksys Etherfast user guide:
"1. I need to set a static IP address on a PC.
The Router, by default, assigns an IP address range of 192.168.1.100 to
192.168.1.150 using the DHCP server on the Router. To set a static IP address, you
can only use the ranges 192.168.1.2 to 192.168.1.99 and 192.168.1.151 to
192.168.1.254. Each PC or network device that uses TCP/IP must have a unique
address to identify itself in a network. If the IP address is not unique to a network,
Windows will generate an IP conflict error message."

That way you have DHCP available (it will assign IPs from the pool), and you can set a machine to use it's own static IP out of that pool.

(On a sidenote: my SMC router has an option to assign from the DHCP server a static IP to a given MAC address.)