I link the netgear router to the incoming BT HH3.
Sure i will be proved wrong but what I do using the HH3 as the master but for you the slave (second device) so the other way round.
Look at the ip address of the o2 router, something like 192.168.***.***
as a guess. See where the top and bottom DHCP ip address are, will be a top and bottom range on the last set of 3 digits. 192.168.***.***, last 3 numbers.
Write that down.
Now go into advanced settings on the BT HH3 and Home network, IP addresses.
Turn off the DHCP server by the tick circle to NO.
Then change the HH3 address to 1 above or below what you wrote down for the o2 box settings so this now is something different to the set one. like this on mine but you will need to change to suit what the o2 box is set to. So wont be like this but this menu you need to find.
IP Address: 192.168.1.254
Subnet mask: 255.255.255.0
DHCP Network Range
If you change the IP address range, you must renew the DHCP lease and or static IP addresses for all devices on the network
192.168.1.64 - 192.168.1.253 (Default)
172.16.0.64 - 172.16.255.254
Lease time: Days Hours
Valid leases are between 1 hour and 21 days
this above is what HH£ does by default (I guess as never changed), you will need to det to suit the DHCP range of the o2 box and go one below or above but not the o2 box static ip adress.
work for me but doing the other way round.
Than link the 2 with a network lead, we can get for a pound in our poundland downtown.
Use on of the 1 to 4 ethernet holes in each box on the back. I find hole 2 on the HH is the best and most responsive of the 1Gig connection. my system nothing like that but made a difference to internet speedchecks if using that hole on the hh, labled 1 gig or something like that.
Then turn off the wireless on the o2 box or if landlord lives there leave on and just have 2 wirless signals going.
HH set to auto on wireless picks a good channel, this all works for me.