homebroo, there is a quick render preset under the render tab, if you increase the resolution on this one a bit you can get a quick render to see how it's going. Unless you have an insanely complex scene of dense clouds and populations this should only take a few minutes, also reducing GI settings, turning off ray tracing, detail settings and atmosphere samples will speed up your render although the first two will alter the lighting of your scene so it will look a bit different. But you have to remember that Terragen 2 is a LOT more advanced than 0.9. Average medium complexity scenes will take around 20 hours to render for final versions, that's why you need to find a quality setting that is quick enough for you and is still high enough quality that you can see the changes you've made. High resolution, high detail renders aren't designed for early testing of scenes, only for finalized scenes.
As far as the memory requirement. For more complex scenes you will require more memory, but because it is of yet a 32 bit application you are limited to 4GB even on a x64 operating system.