The firewall is only active between the switched ports and the "WAN" connection. If you'll be shareing files/printers between devices connected to the switched ports, the firewall will not get in the way.
The LinkSys allows you to specify one IP address for full pass-through (WAN/outside to LAN/inside). The option is available through the Advanced menus. You can also allow specific IP ports to pass, or you can block specific inside IP addresses from passing to the outside (like a print server).
Good Luck
Scott