I have been researching about this but still somewhat confused.

I'll be arriving at Brussels-Midi via Eurostar. I need to get to Brussels-Centrale. According to Rick Steves guidebook, there is a direct train that serves between the 2 stations and it's just 1 stop? This seems to be the fastest option, and a lot easier than changing lines on the metro. Can anyone confirm this (the direct train route)?

Also, will my Eurostar ticket cover that trip from Midi to Centrale? Or do I have to buy a separate ticket for that?

If I take a cab instead (I arrive at noon on a Sunday), how much will it be?

95% of all trains passing Brussels, pass by the 3 main Brussels stations: Midi (=South), Centrale and North. So yes, there's a direct train line and lots of trains (the only thing you have to make sure is to get one in the right direction . I'm not sure if you need a new ticket, maybe somebody else can tell? But I'd just pretend to be an innocent tourist who didn't know you had to buy an extra ticket if it appears to be so

There are dozens of trains per hour that, upon leaving Midi, stop at Centrale on their way north. Your Eurostar ticket is good for onward transportation anywhere in Belgium, so it will certainly be good for this 2 minute journey. In any event, in that short time, nobody is likely to ask to see your ticket.

Great! Thanks stardust & ron. Just exactly what I need to know!

I followed what stardust & ron suggested and it worked out like a charm. After getting off the Eurostar, one has to walk all the way out to the main station lobby, before one can get onto any other train platforms (it makes sense as the Eurostar is an "international" train and they don't want random people stumbling on it). Once I got to the main lobby, I looked at the departure board and caught the next train to Central. As ron mentioned, the Eurostar ticket is good for any Belgian station. The ride to Central station took 3 minutes.