Bruxelles 1000 registration

First and importnat tip: move to another commune if you still have a chance!
On a serious note: it depends on whether you are EU citizen or not, and what is your reason of being in Belgium ( work, family reuniun, studies etc etc.). For EU ppl it is pretty much straight forward just need to wait. If not, prepare to be insistant, inventive, and to know the laws: they often try to screw people and delay things, and not to give what you need. So when you confront them with the law, they get confused and usually give what you need. And yes, ask always name of the person you are talking to and remember faces: it helps a lot if you refer to some concrete person. Because every new person you speak to, tends to invent new stuff...
Do not know if it is helpful, but this expereince I had.

I don't know if the new appointments system is working, but (at least) until earlier this year you just had to get there before the office opens, so 6/7am, and queue. Not much fun at this time of year, I realise.

So if you already were there - welcome to hell :-))
I would agree with SOHCAHTOA, if you go there you need to be there before 8:00 (the earlier the better). From my experience if you come there at 7:30 that would be enough to be one of the first 10-15 ppl.
I heard and the web-site http://www.brussels.be/artdet.cfm/7410/Registration says that the 1st registration should be done on-line . But I would go there and try to register in person - you never know it might be possible... If not, register on-line, wait couple of weeks, and if no anwer, go there and insist to be registered or at least ask what is the waiting time - they have to give you answer.
Best luck and lots of patience.

second the 'come VERY EARLY' - friends showed up as of 6 / 6.30 am ...and take a good book / e-reader / your language lessons ;-) for a possible long morning wait.
Good luck xl