Well since you have 2 different XBL accounts (gamertags) you should be able to just plug both consoles into the router and logon to both accounts no problem at the same time.
Are you having problems getting both to logon or something?
My ? is how can I get both of my Xboxes (1-reg and 1-360) on XboxLive at the same time with 2 different GT's?
I have DSL(AT&T Yahoo), going to a 4 port router. the whole system is wired.
hyghwayman (GT-Umbrella CEO)