Before a user can log in to egroupware, you have to log in with your admin account in egroupware, click on the "Admin" button (located on the upper horizontal toolbar) then click "User accounts" and create the account for that user. You'll have to enter the LoginID (which should be exactly the same as the SME user account) but don't enter the password in egroupware. Also make sure the email address is exactly the same as the SME email address.
AFAIK there is no possibility of synchronizing accounts at the moment.