Just as well Eurostar stopped at the end of the line, or who knows where I might have gotten out. (Did I mention I have enough sense of direction to get lost in a phone box - the old fashioned red kind - I push every door but the right one trying to get out . .. maybe you can see why travelling alone was kind of daunting)
However, I did as was recommended and "followed everyone else".
I found the station concourse easily and although I checked all the recommended departure boards, and found the train for Antwerp and Essen (I think), I could not find one that showed Vilvoorde. Rather irritated with myself that I couldn't even do something that simple, I queued up to ask the information man. He told me platform 20, but when I got there, there was a typical "London" scence - notice up saying in French "do not board" and lots of harassed commuters (it was now after half four in the afternoon) asking where to go and running this way and that; and harassed officials talking animately but doing nothing
Decided that I would not risk just following everyone else, so went back to the information man (after wandering around, hoping to see a timetable that made sense; but I gave up on the time tables. They are in three languages, and worse have domestic, intercity and international trains. I had this irrational fear of getting on a train going non-stop to Russia (Siberian, even), so decided that I'd have to go back downstairs and plead ignorance again.
This time I was amused - my pronunciation of "Vilvoorde" (in Dutch it sounds like "feel-four-duh" - was good enough for him to answer me in Dutch. I had to humbly ask for the info in English, and this time was directed to Platform 17 for the 16.28.
Looked the right sort of train (grin, how would I know) so on I jumped. I was reassured going passed the "red light" area, as one other forum reader had described it, so thought I must be going in the right direction (and I had a PC print out showing the stations along the way. Whew time to relax)