How do I configure the Ooma to keep it from creating a secondary network? ...or at least allow the two computers to share files and printers again? I would prefer not to have to by a switch or other additional equipment.
You could run another cable from your router into your home, or add a Switch to your LAN configuration. A switch is a network port multiplier. The network cable that is plugged into the Ooma device can be used as a feed and be plugged into the switch. Than you can plug your computer and Ooma device into the switch, plus other network devices that you might want to add later, up to the number of remaining ports that you have. The switch will distribute same LAN, router IP addresses. Than you will be able to use the two computers and share files and printers again.
An eight port switch that I like is a Cisco SG 100D-08 8-Port Gigabit Switch.
http://www.buy.com/prod/cisco-sg-100d-0 ... 86031.html
But there are several other switches out there including four port switches.
http://www.cyberguys.com/product-detail ... age=page-1
One goes at each end of the cable. It uses the unused wires in the cable to provide the second connection.
Telo with 2 Handsets, a Linx, and a Safety Phone
Telo2 with 2 Handsets and a Linx
There is software that you can buy to install on both computers. But the software would probably cost more than either the Network cable or the Switch. And I don't think you'd be happy with the software.
Running the network cable through the attic would probably be the cheapest if you are able to do it yourself. You can purchase the network cable already terminated on each end. You can purchase wall plates, receptacle, and adapters, on-line. (In the fall, I just finished routing a few network cables from the basement to the first floor, than through the attic to six locations in our home. Two of the runs were 100 feet long. It's not hard, but it's kind of a pain. I still have to patch the plaster and touch up paint in one place where I installed a new receptacle box, behind a couch.)
For me I'd purchase a switch, because than you'd take care of your present problem, and would have room to add more network devices later.
For example, configure your router to assign 172.27.35.100 through 172.27.35.120, and the Ooma to assign 172.27.35.121 through 172.27.35.140. Note that these two ranges are in the same subnet and must not overlap. Or similar ranges in the 192.168.0.x. This may solve your problem without additional wiring or hardware.
I have not tried this, though. Depending on the firmware in the Ooma, it may not work at all, or may require that you also set up some port forwarding. But it's something to try.