I tried to use the screen capturing, but the frame rate drops and Jinx! stutters

Screen capturing within Windows is very cpu intensive, windows has to synchronize the whole display with all visual effects before it can take the screen shot which will be used by Jinx! (or any other application that uses screen capturing). With active desktop effects like windows aero the time a single screenshot/capture needs is extremly high. So if you want to use screen capturing without getting a too high cpu load or timing problems, be sure to switch off the desktop effects (especially aero) within your windows.