If you have the Email functionality enabled on your forum, when a user registers it will email them a welcome message along with the password they chose. What that mod does, the one Ribkick is reffering to, is it sends a random generated password to the users email address. So the user can't use the forum until they get that email with the password.
I had recently updated that mod with a fix, but don't know if Gor has updated the zip file just yet. So those 2 downloads are the latest versions of the mod.
Yes, as usual Davio is correct. I prefer the random password mod to the built in eMail service because it assures the new member is using a valid eMail address. Good luck.