Wannabe, two things here. One, if it's the old-style radio kit, they really all pretty much work alike, once you've figured one out, you should be ok for the rest. Only thing (in my experience) to watch out for is the audio panel which, especiallly in older/tireder a/c can have its quirks...
Two, re the GNS 430 and up (i.e. integrated boxes), they really require some training. This can however be done at home by downloading (or getting the CD) of the free training software. Check out the Garmin website (I'm only familiar with the Garmins, but imagine the others to have similar programs).
HTH