in reply to Does this user exist?

grinder is correct. Anonymous Monk is, too. Be afraid. Be very afraid. One additional thing to consider is to check the usernames for validity. You do not want a user asking for the name evil::0:0: (of course, the 'name' doesn't matter).

Do the people really need full accounts? Can you create web-accounts (e.g. using htpasswd/.htaccess in Apache)?

BTW, using folders in /home is not a correct algorithm: at least root does not have a home directory there.

HTH, --traveler