I've been looking into embedded ARM systems with ethernet lately.
The Pandaboard & Beagleboard are completely out since my embedded RTOS application has no USB stack.
The two boards we're dealing with are the TS7800 and the Gumstix Overo series. For you, the Overo on a Tobi Duo is a reasonable way to get dual ethernet, though it's only 100mbit. The 7800 has only a single gigabit.
The abundance of embedded ARM devices is really a great thing for small projects. A small, passively cooled ARM computer can do most tasks that you'd have needed a 1U rackmount system for only a few years ago.
As well, they're great for learning. Bootstrapping an operating system from nothing is far, far easier on an ARM system than an Intel/x86 one.
Implementing an operating system isn't that different between the main CPU architectures. I think mcpherrinm was just saying that you have to do a lot less work than for x86, for example, in order to get a minimum of functionality.
Unfortunately I don't know of any guides on implementing a toy OS on ARM. The operating systems course I've taken was a decent starting point, but it mostly deals with theory: [0].
There's also a first year ARM architecture course: [1]
Another course I've taken was about ASM programming on ARM, plus programming some simple hardware[2].
I'm not sure how useful are those materials for someone not taking the courses, but they might offer a list of things to look up somewhere else. Wikipedia actually has some good background theory.
Finally, you might look over the ARM port of EDK2[3]. EDK2 is a BSD-licensed implementation of UEFI[4]. It implements a lot of the functionality of a regular operating system, with the notable exception of multithreading. I find the source code of EDK2 to be easier to understand than the source of the Linux kernel. Probably because it is a lot more lightweight. You can run it on BealgeBoard, by the way. I'd say it's alpha quality software at the moment, so you might get some weird bugs.
Disclaimer: I'm a CS student at Manchester University and I work on EDK2.
The Pandaboard & Beagleboard are completely out since my embedded RTOS application has no USB stack.
The two boards we're dealing with are the TS7800 and the Gumstix Overo series. For you, the Overo on a Tobi Duo is a reasonable way to get dual ethernet, though it's only 100mbit. The 7800 has only a single gigabit.
The abundance of embedded ARM devices is really a great thing for small projects. A small, passively cooled ARM computer can do most tasks that you'd have needed a 1U rackmount system for only a few years ago.
As well, they're great for learning. Bootstrapping an operating system from nothing is far, far easier on an ARM system than an Intel/x86 one.