Layout of a Cisco 67x Router: Top-Down View:

| |  o  o  o  o  o  o |  |
| | o  o  o  o  o  o  |  |
| |  o  o  o  o  o  o |  |
| | o  o  o  o  o  o  |  |
| |  o  o  o  o  o  o |  |
| | o  o  o  o  o  o  |  |
| |  o  o  o  o  o  o |  |
| | o  o  o  o  o  o  |  |
| |  o  o  o  o  o  o |  |
|  -------------------   |
|                        |
|  ____________________  |
| |  0  0  0  0  0  0  | |
|  --^--^--^--^--^--^--  |
     |  |  |  |  |  Power (Green)
     |  |  |  |  Alarm (Red)
     |  |  |  Lan Link (Green)
     |  |  Lan Activity (Yellow)
     |  Wan Link (Green)
     Wan Activity (Yellow)

My explanations of the lights (if they are on):

Power: The Modem/Router is connected to a power source properly

Alarm: Something is wrong with the router (Bad Thing)

Lan Link: The Modem/Router is properly connected to an Ethernet NIC or a hub.

Lan Activity: The Modem/Router is communicating with your computer or internal network.

Wan Link: The Modem/Router is trained (connected to the CO)

Wan Activity: The Modem/Router is talking to the ISP

And if they are not on:

Power: The router is not receiving power

Alarm: All is well internally

Lan Link: Either the computer connected to the router is off, the hub it is connected to is unplugged, or there is a problem with the cabling

Lan Activity: Your Computer is not actively talking with the router (not necessarily a bad thing).

Wan Link: The modem is not trained.

Wan Activity: The router is not currently talking to the ISP.

And from the back:
  __|    ___________________  |__
 |  __  |    |    |    |    |    |
 | |o | |____|____|____|____|    |
 |  --   ENET MGMT WALL PHONE    |

What the ports are for:

ENET (Ethernet): Cat-5 network cable goes here

MGMT (Management): a piece of cable with an RJ-45 connection on one end and a 9-pin serial connection on the other goes here (the RJ-45 end) used to terminal in to the router.

WALL: Phone Cord goes directly from here to the wall.

PHONE: You can connect a standard telephone into this jack.

Cisco has released two routers in the 67x series, the 675 and the 678. The 675 will only work in CAP mode, while the 678 can do both CAP and DMT (a bios flash on the router will switch it from one to the other).

The 67x series came into Cisco when they acquired Netspeed. For the operating system, the routers run an updated version of Netspeed's NBOS called CBOS. The current CBOS version we're supporting at my company (DSL line support) is 2.4.1

Current rumor is that Cisco is getting out of the CPE business, and the 678 is the last DSL modem/router they will release.
More Info on the 67x: