What Zaladane wrote is true. Any modern Netbook is close to the performance of a mid-range computer from 2001. You'll be able to play most games from 2004 and below. Of course, it always depends on how advance they get, but in general, you should be able to play any game before 2004.
Empires: Dawn of the Modern World was pretty good, if you cap the tech tree before WWI. That one might be a little too much for a Netbook though,