Access Conversion of Multiple Excel Files

This project will include combining multiple excel worksheets into a single database. We will need several (3-6) pre-set reports. We would prefer data entry forms to be similar in lay out to our current excel worksheets. Most of the information is text, numbers, with some simple accounting formulas. We will require multiple users with different levels of security access and reporting abilities. Security is a must. We are currently not using access but we have 2003 professional office. Will we require upgraded software for multiple users at the same time?