Networking: How to add another router

[Geoff Shang]

Hi,

I find myself with the need to connect 5 ethernet devices to 4 available 
ports.

I'm running an ADSL modem/router with a 192.168.2.x network (for 
historical reasons) and have allocated static addresses to all of the 
static devices, and a pool of DHCP addresses for devices which ask for it.

Right now the fifth device is running on wireless but I want to plug it in 
if I can.

A quick Google tells me that there's no kind of double adaptor available 
to help solve my problem.  The closest I've seen is a way to send two 
10/100 mbps Ethernet feeds down the one ethernet cable, but you still need 
two ports at each end.  I only have one so that's no good.

Assuming that there is no such double adaptor device that I can use to get 
me a fifth port, the only solution I can see is to drag out the Edimax 
router I have here which is no longer being used.

Assuming I do this, I'm wondering how to configure it.

I'm guessing that it will actually have to route.  I can't see myself 
doing bridging because there'll have to be two devices on it (the router 
will need to take up one of the 4 ports on the modem/router so this then 
leaves 5 devices and only 3 other ports,).

Presumably I need to configure the WAN port so that it connects to the 
existing network.  Do I need to set aside a subnet of the 192.168.2.x 
network specifically for the second router, or can I just enlarge the 
entire network and have it all just cope, with the right packets going to 
the right places?

My preference would be to be able to keep it all as one big network, as 
I'd rather not have to reallocate static addresses if I can help it, which 
I'm guessing I'd have to do if I had to make the second router have its 
own subnet of the 192.168.2.x network.

Netmasks and such tend to confuse me a little and I'm not sure what I 
should be doing here, so any suggestions would be helpful.

Geoff.