VBA user/password form to vary access

Hi,

I have a complex workbook that has 20 sheets.
5 are used to input data
15 are used for various types of reports etc

I curently have a single username/password form that provides general access to the workbook, What i want to do is allow multiple usernames with individaul passwords. Ans also allow diffenent people varied access either by checkboxes or have access based on their username.

I have been trying for ages but no luck...thanks in advance