To be honest I would just use mixed mode. The extra nice things like password aging, encrypted passwords and the NT/200x security model will be avaliable to the users that you allow to use windows logins, and will not be availiable to SQL Server logins.

there is a chap named Neil Pike who runs the UK SQL Server users group that may be able to help you out.

his site is http://www.sqlserverfaq.com/ and he has an extensive KB and FAQ section there.