Please tell me the best way to get from the Brussels S. Charleroi airport to Brussels Int'l? Time is the most important element. THanks.

I don't think there is a direct bus from Charleroi (it's not really Brussels South, no matter what the marketing boys tell you) to Brussels Intl (Zaventem), hopefully someone will correct me if I'm wrong. I don't use Ryanair (heard too many stories about bad experiences, don't like their underhanded advertising schemes or their policy toward wheelchair travelers)
Probably the easiest thing would be to take the bus to Brussels Gare du Midi (Brussel Zuid) and then pick up the airport express train.
The fastest way would be to take a taxi from one airport to the other, but it's very expensive.
BTilke (Brussels)

The train from Charleroi to Brussels Int.Airport takes 1h20 minutes with a change in whatever of 3 main Brussels railway stations (South, Central and North). There's a train at .07 and .34 past the hour. Local bus 68 takes you from the Charleroi airport to the train station, but if you're in a hurry, a taxi is probably better. The train is in my opinion also the most secure way to get there on time, as traffic jams can get pretty big on highways around Brussels! Check www.b-rail.be, Charleroi-Sud and Bruxelles-Nat-Airport are the stations you need.

Stardust, does the train leave from Charleroi airport or from Charleroi the town? I know the Ryanair bus leaves directly from Charleroi airport and drops you off at Gare du Midi. If the train doesn't leave from Charleroi airport, I think the Ryanair bus is the better option as Ruby74 is probably coming in on a Ryanair flight.

The train is from Charleroi City, not the airport. It's 8.80€ one way. Travel times will probably depend on the traffic. In general I'd say if you're planning to make the journey between 6.30-9.30 am or 4.30 to 7.30pm the train is still the best option (due to high traffic)

Thanks folks, that was very helpful - - yes I'm coming in by Ryanair and need to catch a connection.