OK, just built a new PC cos the ASUS pundit has stopped working and I was fed up of not being able to use my OPUS. The general idea was to get as much as possible in the C137 case including the OPUS. In fact the only thing I kept external was the media drive which I've put in a USB 2 caddy for easy removal and loading.
I like a bit of grunt in my PC, so I used a mini-ITX P4 motherboard with a celeron 2.4 ghz and 512mb RAM. Using the low profile 40GB disk for booting and apps, I can get 2 PCI cards inside and the OPUS.
Here are some pics...
The OPUS nestling where the old 120W psu used to live, its not fitted in properly or wired up yet, but you can see there is plenty of room.