Here is the more compact, "bb'd" form of the Bit Torrent configuration rules for dual WANs and two computers. Seems to work fine.
! saved at 2013-01-04 18:12:50
! model: ZyWALL USG 50
! firmware version: 3.00(BDS.2)
address-object BT1 192.168.1.102
address-object BT2 192.168.1.103
!
service-object BT1-TCP tcp range 52890 52890
service-object BT1-UDP udp range 52890 52890
service-object BT2-TCP tcp range 52891 52891
service-object BT2-UDP udp range 52891 52891
!
object-group service BitTorrent1
description Bit Torrent
service-object BT1-TCP
service-object BT1-UDP
!
object-group service BitTorrent2
description Bit Torrent
service-object BT2-TCP
service-object BT2-UDP
!
ip virtual-server Bit_Torrent_1to1 interface wan1_ppp original-ip any map-to BT1 map-type port protocol any original-port 52890 mapped-port 52890
ip virtual-server Bit_Torrent_2to1 interface wan2_ppp original-ip any map-to BT1 map-type port protocol any original-port 52890 mapped-port 52890
ip virtual-server Bit_Torrent_1to2 interface wan1_ppp original-ip any map-to BT2 map-type port protocol any original-port 52891 mapped-port 52891
ip virtual-server Bit_Torrent_2to2 interface wan2_ppp original-ip any map-to BT2 map-type port protocol any original-port 52891 mapped-port 52891
!
firewall 3
from WAN
to LAN1
destinationip BT2
service BitTorrent2
action allow
!
firewall 4
from WAN
to LAN1
destinationip BT1
service BitTorrent1
action allow
!
I think earlier I was hesitant to allow "all" rather than just "TCP" and "UDP" to the opened ports, but ICMP doesn't use a port, and in any case, iptables on each computer's firewall is only set to allow UDP and TCP at the BT port.
kirby