Does it have to be split screen, or can just be a game that you can play with multiple people on the same computer (AKA Hotseat)? There are very, very few new games for PC that allow for Hotseat, since most PC games require a network of some sort to play with multiple people.
My best recommendations are:
The Battle for Wesnoth (The most recent I can think of)
http://www.wesnoth.org/
Star Control 2: The Ur-Quan Masters (old game, but remade to work in Windows)
http://sc2.sourceforge.net/
Tyrian 2000 (1999)
http://www.abandonia.com/en/games/296/Tyrian+2000.html
The Settlers (1993)
http://www.abandonia.com/en/games/288/Settlers+1%2C+The.html








