RuthChan, I've lived in Brussels for 23 years so if you need any particular advice nearer the time, please get in contact. I agree about the BCT. When my boys were little it was a life saver as all the Belgians I had got to know went back to work a few months after their babies were born. (I'm actually still a member of the "Lifers" group.) I got by with no car until my eldest was nearly 11 (and we decided to have a third child) but what I found was that although we had no car and lived close to a metro, other mums didn't so the travelling to coffee mornings could sometimes be lengthy, especially with two little ones. The BCT is also great for giving advice on doctors, dentists etc so please join them as soon as you get here (if not before!). www.bctbelgium.com/
Choose where you live carefully. Do you know where your husband is going to be working, as it would be a good idea to make sure you're either not too far away or on a metro or tram route as the rush hour traffic can be horrible? There are definitely some areas to be avoided though so if you do get some idea of where he's going to be it would be a good idea to come on here again and ask for advice.
There are also some English primary schools in Brussels itself as well as one in Vossem and the British School in Tervuren. These are the Brussels based ones: www.bjab.org/ www.bisb.org/ www.beps.com/
All English speaking schools are fee paying though and as there are no tax breaks or concessions from the Belgian government they are not cheap.
I actually live on the road (in Auderghem) where the Japanese School is so I'm sure I could find you some information about that if you're interested.
It is possible to get by with English but I teach French to some of the mums at the British School and they find the fact that they can't communicate with the plumber somewhat frustrating. I would definitely suggest learning Dutch and not French though if you end up living in a Dutch speaking area as it's only really in Brussels itself that both languages are used, or at least expected to be used.
Signing into the country in the local town hall can be a bit of a pain, especially if you struggle with the language but you will be expected to do this. There is quite a lot of red tape to get through here to start with but it's pretty okay once you've sorted it all out.
Driving isn't the best here. I still don't like it after all this time here. The drivers aren't very considerate and completely ignore pedestrian crossings. And of course, as you say, MrsSf, there's the infamous "priorité à droite".
Having said all of that, it's really an okay place to live!