I assume you deploy your solutions to sharepoint document library.
Your solution should be in setting proper permissions for certain sharepoint groups. Permissions are easily assignable. For more information:
http://office.microsoft.com/en-us/help/HA100215641033.aspx
For other part you would need to deal with views. One solution would be to create only personal views for all users, which in your case would not be big hassle since you do not have many users. In those personal views you set filters to display for each user what she/he needs to see. But as said it is not elegant solution.
Unfortunately there is no easy way to set permissions for views in sharepoint 2007. It is however possible to programmatically customize it by adding some javascript to your page.