Hi, I accidentally deleted the database of users whilst making some changes. Is there any way to recover the users and passwords or do I need to re-enter them?

If you had no backup, unfortunately there is no way to recover that data.
Sorry......

Did you delete the users from the program? Or did you delete the file from your hard disk? If you deleted the file from your hard disk, there are ways to recover it. This is just 1 of many...http://www.piriform.com/recuva
If you deleted the users from the program, as Scott said, sorry.

Oops! Yes it was from the program so I giess I have to start all over again! Is there a way to make a back up to go to if I am stupid enough to do this again?

Yes! In WAM use 'File/Backup Website Profile' to create a backup.