From reading your post, I'd say perhaps some of the training tips I've given Rob regarding his Toby on his thread could help you get a start on changing your little guy.
I'd be sure his daily life is enriched with regular obedience training at home x5 mins. twice a day(an absolutely necessary tool for reshaping the behavior of dogs who are extremely headstrong if you keep it fun and upbeat for them), he gets time with puzzle games you invent for him and toys, his food is served in kong or other toys where he has to work to get his meals out as terriers love to seek/hunt out their food, plenty of extra exercise to work out his stress/tensions and is started on one of the Nothing In Life Is Free programs which he will grow to adore as dogs just love to show us they can perform smartly in order to get what they want. They really get into NILIF and it makes both your dog and you so proud of how quickly they come to obey your command or request in order to get their needs met and, in the process, your pack/family leader roll is strongly reinforced in his eyes through this program.
Then, I'd practice the training tips on the thread below with your little Buster and show him new boundaries are now in place and gently but firmly and persistently retrain him into finding a new way to accept dogs being in his presence. Walking him on the lead is a wonderful way to teach these techniques initially.
http://www.yorkietalk.com/forums/gen...ks-please.html
Once he's made advances with accepting other dogs, then we can work on his accepting humans in much the same way with some tweaks but one thing at a time.