Filemaker Pro is a database package that runs on a client machine, and provides an easy-to-use database capability. Users can typically manipulate the data in a variety of ways. Data is stored in files on a local machine or on a network.
SQL server is a back-end product. It is a database engine which controls the storage of data, and uses a standard language, Structured Query Language (SQL), to communicate with any of a huge number of outside client programs, including custom-written VB programs.
With Filemaker Pro, users pretty much can do anything they want to the data, including changing it or deleting it (intentionally or not).
With SQL server, a lot depends on the client you chose to buy or write. If you write a VB program which uses the security built into SQL Server, you can limit users to which fields they can see and/or change according to their login. SQL server also has provisions for automatic data backup and recovery, transaction checkpointing, and a host of other "real" database features.
My personal feeling is that there is no way I would use Filemaker in a 100 user environment. I would want my data in one place, and I would have my users able to only use that data in ways that I could control.
Links:
SQL: http://www.microsoft.com/sql/
Filemaker: http://www.filemaker.com/index.html
(remove any spaces in the above links).
Good luck.
