Sorry I dont understand what you mean by "if you used a fixed initial keyword", so I think the option of sending out a bulk newsletter telling all the users to retrieve their passwords is the best option

Ahh, understand, what I have had to do, the spreadsheet that I have with all the user details, I randomly gnerated on in the spreadsheet the username, so I just copied the email address to the username column.  I then imported all the details and mass emailed the users with instructions to use the retrieve the password option, to get a new passwoord, login and change it, simply really when you have a coffee and think about it, thank you guys for all your help.