You will never get 'N speeds' on G hardware.
The 802.11g supports max. 54 Mbps; this is defined in the standard and can never be more.
If your N-router supports 802.11g then there is no need for a second router.....I would hook up the consoles to a switch.
Connect the switch to the N-router.
That should work.
Your switch ports should be FastEthernet (100 Mbps) or else you are stuck at 10 Mbps