Hmmmm... we'll I've got something that I thought should work but seems pretty broken:
https://dl.dropbox.com/u/10783986/ecu-reader.ino
I tried hooking it up to the ECU and no luck at all... doesn't see any packets at all. If I hook it up to another Arduino running the simulator code I saw on the SV forum, it sees data; but only if I change it to 9600 baud (the emulator is running at 7800?) Even then though, things are broken- seems like I'm missing occasional bytes on the wire and looks like the data is corrupted.
Not sure if this is a limitation of the SoftwareSerial library or if my code is subtly broken. I looked at the limitations about the library on it's web page, but since I'm using an Uno and only one pin for serial, it doesn't sound like either apply to me.
Anyways, hopefully the logic analyzer I ordered shows up tomorrow and I can see the ECU protocol for myself rather then relying on some descriptions by other people.