Run Router Run! WRT54G v3.1 Information about vlan ports.

WRT54G v3.1

In OpenWRT, you can configure that by editing:

/etc/config/network

config switch eth0
option vlan0 "0 1 2 3 4 5*"

Now, I was stumped as to which number corresponds to which port, found the information on DDWRT's website [1]

0 = WAN / Internet
1 = Port 1 (nearest to WAN)
2 = Port 2
3 = Port 3
4 = Port 4
5 = CPU Internal
5* = CPU Internal default

It is worth reading up on the details of what 5 and 5* ports mean, on the original website:

[1] http://www.dd-wrt.com/wiki/index.php/VLAN_Bridging_WAN_and_a_LAN_port