Untill July 2003 these things used to be done at several adminustrations.
Since July 1st 2003 the Belgian administration has introduced the 'company guichet' 'ondernemingsloket'.
This means that for all administrative matters with the govenment a company should address itself only to one location. So it's possible to ask there for VAT number and regustration the the regsiter of trade.
Often the founders of the company give a power of attorney to an accountant, who will take care of these adminustrative obligations.