This week I discovered that you can add more than one sun in Terragen 4. This is exactly what I was looking for.
Below is a little render illustrating a possible planet orbiting Alpha Centauri A. The presence of earth-sized planets or super-earth worlds in the Alpha Centauri system is not yet excluded, but such planets still remain to be discovered. Each of the two stars has zones around it where long-term stable orbits are possible. For the sun-like Alpha Centauri A, this zone extends to about 1.1 times the Earth-Sun distance.
Alpha Centauri A is older and more luminous than the Sun. This means, an earth-sized planet even near the egde of the stable orbit zone would receive so much energy that is is likely to be an end time world - a desert world, locked in an escalating greenhouse climate and losing it's water into space. Heat-resistant organisms might still hold on for some time.