As far as I remember it's just a question of modifying the m2network.ini file on the master machine to point to the other's IP address.
Master Machine's m2network.ini
[Network]
RxPort=1979
NextIP=192.168.0.2
NextPort=1978
Where 192.168.0.2 is the IP address of the slave machine.
Then you need to ensure that you select the first machine to be 'Master' and the second to be 'Slave'. Using the key mapped to 'Test' (mine is F2), use the VR1 button to move up and down the menus until you can select 'Game System', press 'Start' to select it. Then move to Link ID and change it to 'Master' (using 'Start' to cycle through the options).
Repeat these steps on the second machine but select 'Slave'.