In reply to The Lemming:
Registax is an old program now and it might not be able to use all your RAM and features in a modern computer anyway. Traditionally it worked well with webcam images which were 640x480 pixels or similar or modest astronomical CCDs and as Andi says, chugged along fine with that and produced some great images.
If you start throwing 6000x4000 pixel DSLR images at it, it may well grind to a halt because the program might not be able to handle the 100+ mb individual frame images
The moon is a good target as it's so bright you can use movies (eg at 25 frames a second) and still get good images. This allows you to take hundreds or thousands of frames for analysis and the software does a good job of picking the best bits from each frame. I would imagine that a 1920x1080 movie from a DSLR should just about be within its capabilities but it might thrash away for a while processing.
An alternative program you could try is avistack.