wrt54g 2.0
interfaces -
lan - vlan0
wan - vlan1
wifi - eth1

first, make port4 into a new interface called vlan2

vlan0hwname=et0
vlan0ports=1 2 3 5*
vlan1hwname=et0
vlan1ports=0 5
vlan2hwname=et0
vlan2ports=4

(you'll need to commit and reboot before the ports get remapped)

now, the lan and wifi are separate segments

lan_ifname=vlan0
lan_proto=static
lan_ipaddr=192.168.1.1

wifi_ifname=br0
wifi_ifnames=eth1 (wds links are added to br0; if wds is disabled just set wifi_ifname=eth1)
wifi_proto=static
wifi_ipaddr=192.168.2.1

now, the wan is going to be bridged ....

wan_ifname=br1
wan_ifnames=vlan1 vlan2
wan_proto=dhcp