thanks all for the help.
yes i wanted to use the engine as dll in a c++ program.
i got confused a little bit, because it seems that if you install the free version and use its dll in c++, its the "30-day-demo-dll"..i thought it would either be possible to use the dll for unlimited time(but that would be the engine sdk, just as firoball said) or it cant be used at all, not even for 30 days.