Securing A Small Business Network

Hello! I work for a small business that will very soon be expanding it's computer network from 2 workstations to about 10. Right now we have a Windows XP PC acting as a gateway to connect wirelessly to the internet. I am looking into putting a dedicated security device such as this one between the gateway PC and the gigabit switch that the rest of the network is connected to. My question for all of you is whether or not I will still be able to use Windows XP ICS after inserting the firewall. Can I connect the WAN port on the firewall to the gateway PC, and connect the LAN port on the firewall to the switch and still have access to the Internet? Thanks for your help!