All things are usually possible, there is no ability with SQL to offer a popup facility to change the password out of the box. Dependant on your requirements, you could write something that would do what you wanted, to call the password check them the application etc. At a low level you could get the users to change the passwords through Query analyser or Management studio. I don't know if your users use this or not.
There are ways you could have scheduled checks that the password does not exceed a set time and notify users, either email or net send etc. It really depends on what access they have and how you want to manage it.