jaggy - I agree, my older one always gets the hard end of the stick (not literally, of course ... 
) We always assume he SHOULD already know - without realising how he damn well cannot. Even an adult cannot always deal with emotions, imagine the under 3 year old deaing with changed attention of his dear parents etc.
I guess the central thing is to accept, as someone in another thread put it - "all behaviour is for a reason". Being "naughty" is caused by being more emotional, which is in turn caused by feelings of fear, anger, confusion etc. So in your case it may be that he is feeling distraught by the arrival of the new one who gets so much attention and who has changed his parents and his life (even if only ever so subtly). Now, you can always just try to deal with the surface layer, that is, "being naughty". As you have learned (lucky you! Many parents just won't accept that and set themselves up for a long period of standoffs!), it does not really work. I am sure parents who are "consistent" in punishing their children and banning the show of emotions will get results, too. But they are, in the process, going to undermine their relationship with the child and potentially steer the child in the direction which is leading to other issues later in life. My 5 year old, for instance, has unfortunately learned that showing emotions is a negative thing so gets very irritated by his younger brother's crying, and sometimes yells at him. It's like looking in a mirror for me - as we only recently learned to treat crying and tantruming differently.
Thankfully as we are now consistently responding calmly and supportively to emotions, he is coming round to accept his brother's as well as his own feelings better. Anyway, that aside, it is best to, on the one hand, reassure him of your continuous love and presence for him, and on the other hand, not punish him for tantrums but accept this is an outlet of strong emotions (with often ridiculous pretexts). Some children allow you to hold them whilst they complain and tantrum, some will yell and try to hit. I hold the hand that tries to hit and tell him it is ok to be angry and to cry but not to hit. As he learns that you will not abandon (see below!) him for his emotions, and as you learn to welcome the show of emotions as a way to connect to him rather than as an obstacle in your relationship, he will be less "naughty" and more cooperative. It may take time (it has taken a few months for me to see real results) but it really works.
I can only recommend again to get one of Solter's books or to check out advice on www.awareparenting.com although for me, the books worked better as more systematic etc. But you might find the bits and pieces you need from there.
Re: abandoning. Just a brief explanation -- I realise "abandoning" is a strong word, and I do not mean it literally. On the other hand, for a small person the anger of the parents he loves, and their dishing out naughty corners and other punishments will often feel like abandoning, literally. And it teaches them not that when they are "bad" their parents get mad and then they will feel "bad". No. It teaches them that when they feel "bad" and as a result act "bad", their parents get mad, so it is best to suffocate the feeling of "bad" - which, unfortunately, leads to acting even worse...
Sorry, this was a long one, but those thoughts here just got me thinking. I hope it wasn't entirely useless for the OP!
Best of luck to you all,
M