you'll need the transmission harness and that's it, however, it's wired into the main engine harness and the ECU.
what are you doing for a computer?
also an 06 has knock sensors, so 05/06 harness will work.
04 harness will not work unless you have your knock sensors turned off (via SCT) or drill the block and install knock sensors (can be done, but you better know what you're doing).
the truth is, the t56 will work no matter what because it's purely mechanical. what you won't have (until you wire it in) is reverse lights, reverse lockout, and one other thing that's escaping me at the moment.
you say 06 viper, is it a car or a truck?