But if you have a db with members sat id 1,2,3,4,5,6,7,8 (but loads more like 120,000), the ohter db would have the same id numbers and the entries would be overwriten...

The scripot would need to know the last id number for members/posts/etc then re-number the new db from ther upwards...

For example if i inserted a load of member data from another forum to mine it would overwrite the members that had the same id numbers...