I'll see if I can help you with another one Mick
This is my 'vanilla' registax process:
* Open registax
* Click 'select' and then open all of the pictures you want stacked. I usually select all the pictures I want to stack first and put them in their own directory, then I goto that directory, select the first file, and then shift-click the last file and all will be highlighted
* Your curser will now be a box when you mouse over the first image that is shown on screen, move the box over the top of saturn and click ontop of it to 'mark' it as your alignment point
* Click 'align' (note, sometimes you will lose alignment on a frame, you have the choice to either deselect the frame, or you can also maually put the box over the centre of saturn again so manually tell it where to align to)
* Click limit
* Click 'Optimize & Stack'
* Click 'save image'
Hope this helps!