For some it may come as no surprise but, the classic Command and Conquer games work well on netbooks. The games require low resources and a light installation. Command and Conquer: Red Alert, Tiberian Dawn and Tiberian Sun & Firestorm are free to download from here.
The games can be run by either decompressing the files, or emulating CD images. You can see Tiberian Dawn in action on an Asus Eee PC 1000HE, which like many netbooks, features an Intel Atom N270 CPU, 1GB of RAM and integrated GMA 950 graphics.