You can try single sign-on, but I don’t think this technology is yet up to ‘par’.
You might want to look at a technique called ‘password syncronization’. You still create a user-id/password for each system/application the user needs (the user-id is the same for each access point). The software then centralizes the administration function – if a person needs 5 user-ids, then you create the ids/passwords in this centralized database. If one of the user-id passwords change, the system changes all of them to be the same. The user is still required to login, but the password is the same for each. In this manner, you can ensure that ‘simple’ passwords are filtered out (not allowed). Some of these software products allow you to run scripts to auto-logon users.
This is also very useful when a user leaves the company or you want to suspend the account because all of his/her access points are stored in a central area, and just be changing the password, you deny access.
Another benefit is auditability – you can quickly determin who has access to what applications.
This is not the best solution, but it allows a few people to control large bodies of user-ids/passwords.
There are other issues such as backup servers, security databases, scaleability, etc. If you research this topic, you will discover these and others. You should be aware of some of the negative issues as well.