There are pancake cases for mATX mobos that would fit into something like a catalog case along with an LCD monitor, normal kbd/mse, etc. Here's a link to some at Newegg:
slim mATX cases
Others are available elsewhere and probably also at the Egg as their descriptions aren't consistent at all (you know, those things that searches depend on to work :roll: )... Most of the ones at that link will take only low profile add on cards. There are even slimmer ones which take only one or two add-on cards by means of a card riser which would be at right angle to the mobo (the card or card(s) would then be parallel to the mobo). Plus there are compact pre-pack systems like the AOpen mini (looks like one of the Apple Macs) which aren't much bigger than a standard DVD drive, but a little thicker - they also have the Acer Veriton line now. Depends on what you're willing to give up when you start getting REALLY small... I tried to get my step-sister to consider this idea as she really wouldn't use her laptop as a laptop either - just back and forth between the winter and summer homes a couple times a year, but she wanted the "security" of a name-brand laptop. You can get larger screens on the laptops these days, but you'll pay more of course. Compucase, Enlight and InWin both offer some slim cases. They often come bundled with a PSU, so you have to determine whether that is suitable for your mobo, CPU etc. And MSI has some compact barebones. Probably lots of other stuff out there, but what's here should give a start. The microATX desktop choice under Computer Cases on the Egg will bring up more options.
Directron.com also has a good selection of the low-pro mATX cases and smaller compact systems and cases. Provantage.com carries Acer and AOpen and a few other case lines.
The nice thing about the notebooks is that they are designed for portability. Things like memory, etc. won't pop out of sockets, etc. But you can ruggedize most systems with a little thought, zip ties and hot glue.
.bh.