This post is particularly for any of you that use Access in a multi-user environment.
Selecting the Right Security
When developing in Access to serve multiple users, it is important to consider what level of security you need before you get too far down the path. If you need comprehensive, air-tight security, Access is not the right way to go. Think of Access as a small safe where you keep valuables. You can lock it, potentially bolt it down to the floor, but a skilled thief will simply pry it from the floor, take it home, and figure out how to crack it open with enough time. So if you are highly concerned about data security, look to a more heavy duty platform like MySQL, SQL Server, or Oracle on a centralized database server. If you are satisfied that your employees are not likely to (a) attempt to compromise the data in your database, or (b) take the time to become savvy enough to overcome some basic security measures, Access is just fine.
Securing Your Access Database
Since there are many resources to help you with the necessary tasks of securing your database, I'll just hit the highlights before listing further reading.
There are quite a few resources out there on the details of securing an Access 2007 database. The two that really give you a full picture are:
How I Use Microsoft Access User-Level Security by Jack MacDonald
Real World Microsoft Access Database Protection and Security by Garry Robinson