4 sites one login page

I have 4 sites that use the same user table in a database. How can I set it up so that I have one login page and depending on user.group the user is sent to /vendor.. /customer.. /staff.. or /sales.. ? I suppose I would be dependent on one site for password reminders, or maybe I should create a 5th site for this purpose.
Any help is appreciated,

Peter

Hi,
First make sure every username is unique ! add a constraint in database user table for all usernames to be unique. Secondly, create user groups in phprunner for howsoever you want. And finally while entering the userid you give a selection of what the user type is and add that groupid through your script into the user table groupid. Assign permissions to the entry screens in phprunner depending on user group and finally link the group field to groupid of your phprunner. Thats all there needs to be done !