Thanks for the help all
Is there any other way that I can import/copy all the posts and user details from one forum to another without copying a complete backup of the original forum?
nope, that is how it is done.
did you do what was suggested, did you get and run the cookie MOD on the new board ?
that will find the correct settings for you and then it will all work.
however, from what you described, I am not sure but what you are still working on the original database.
the proper procedure for what you want to do is this.
create new database,
install new phpbb in different folder
go to old board,
backup database to your computer.
go to new board
go to admin panel
restore old database over new one.
now, becuase you used the old database on your new board, you now have the script paths pointing to the old board.
so, run the cookie MOD on the new board,
accept whatever it suggests for you.
then follow the instructions to clear cookies, etc. etc.
now, you should be in business.