I'm no expert but my understanding is that squash/pumpkins are quite promiscuous. If there is more than one variety nearby they will cross pollinate and won't grow true from seed. If you want to save seed you should hand pollinate and then put a rubber band or suchlike round the flower to stop any other pollen getting access.
Jeannine or others will no doubt give you better information in due course.
Once you've got the ripe pumpkins, scoop out the seeds you want to save, give them a good rinse in cold water and spread them out to dry.