Jason
chasing a bee
Wow, are you sure you want to recommend GSC's RTS titles to a strategy newcomer? Or anyone, for that matter.If you can stand old graphics, play Cossacks: Back to War [it's a stand-alone expansion and doesn't really have a campaign, but is superior to the original. The original, Cossacks: European Wars, does have a few campaigns, though, but they're ultra-hard. But the game is pretty awesome, so buy Back To War, it does have some pretty nice scenarios, too].
In the same vein, play American Conquest: Fight Back. Also a stand-alone expansion, including all the features from the original, and it has nice historical campaigns. It's from the makers of Cossacks, the main difference being that it's even more realistic than Cossacks and has better graphics. If you like the period of the American Civil War, too, you can buy the second standalone-expansion American Conquest: Divided Nation [which should still be in stores somewhere, at least here in Germany Media Markt still has it].
Then there's Cossacks 2, which is set in the Napoleonic Wars. I actually liked it a little less than the first Cossacks and American Conquest, but it's still good. Pretty realistic and if you don't know what you have to do it can be pretty hard, too. The campaign is harsh to newbies, but interesting.
I'd go with the obvious choices: Ground Control, Homeworld,Warlords Battlecry series, maybe Dawn of War.
Or skip the whole RTS thing and try the Combat Mission games.