Jack,
I had problems with Nortel Extranet IPSEC vpn client with SME 5.1.2. The following is from a posting from this forum. These commands allow multiple Nortel Extranet connections to pass through 5.1.2. I don't know if they will work for 5.5, but it is worth a shot. Please post if this works for you or not.
Commands:
# /sbin/e-smith/db configuration setprop masq ipsec yes
# /sbin/e-smith/signal-event remoteaccess-update
I had to also check 'disable keep alives' on each client or the connection will fail within a few minutes.
Good luck,
ryan