I worked out another way of centering the bmps last night rather than using ppmcentre. Unfortunately it doesn't rank them but ImagesPlus (for those who have it) does a damn fine job of centering all the bmps prior to dumping them into Registax. Just use the planetary alignment feature.
You will need a good deal of RAM though
. It took a while to do 600 bmps on my little laptop (512 meg ram)