Ok .. Here we go...
Lets make sure the IP Office is ready to be part of your network. Connect your PC DIRECTLY to the IP Office and log in thorugh Manager. Below are the settings that will need to be made / changed in the IP Office.
System - LAN1
* Make sure your IP Address is set to an IP address that is BELOW the range DHCP is assigned and the IP Address is not set for another network device- example 192.168.0.10
* IP Mask - should be 255.255.255.0 - Unless you have changed this in your router.
*Make sure DHCP is set to DISBALED- AS you stated your router is assigning DHCP.
System - LAN2
* IP Address - who cares, we are going to use LAN1

* DHCP - Select DISBALED - Should not make a difference but be safe.
System - DNS
* If you have a DNS Server in your network you would enter this IP Address here... I'm guessing you do not so you can use the DNS supplied by ISP or a standard is 4.2.2.2 and a backup would be 4.2.2.1
Save these changes and reboot the IP Office.
After the reboot bring the IP Office back into your network... Your connections should go something like this... Cable modem to Router, Router to IP Office any of the LAN 1 PORTS!! not WAN! and just standard cat5 cables are fine... no crossover.
~Quick Note~ You could connect modem to IP Office to router... just as long as they are all connected together.
Make sure your setting on your PC are either set to a static IP that is available or you have it set to obtain automaticlly...
You should be good.. Internet should flow through modem to router and though IP Office.. you should be able to use any of the LAN 1 ports for internet traffic.
I think this is all of it... anyone see anyting I'm missing?
*** NOTE ! *** If you are upgrading / downgrading the manager firmware on the IP OFfice you SHOULD ASSIGN STATIC IP!!! VERY IMPORTANT!
Have a good weekend! Please post any problems / questions... I'll try to check over the weekend.
Take Care,
Tekcetera Support