Any application that will entail a web browser interface and tie in to a database backend will not be simple to deploy. Perhaps you already realize this, but installing and configuring a web server (i.e. Apache), a scripting language processor (i.e. PHP), and a database (i.e. PostgreSQL) on hundreds of laptops would be a nightmare.
If you have the option, you might consider a compiled executable application for the end user rather than a browser. You'll get the benefit of a richer, faster interface, and deployment headaches would be reduced immensely. The application could still talk to the web database for synchronizations.
Every person will promote their favorite tool and I am no exception: Delphi (
http://borland.com/delphi) is easy to learn but a powerful language and creates native executables for either Windows or Linux (
http://borland.com/kylix). It can talk to several different databases, including my favorite, Firebird. (BTW, Delphi can also be used for web development using three different technologies, including .NET!)
Firebird (
http://firebirdsql.org), which is open source, has an embedded version which is a simple .DLL file to deploy, but can scale up to handle large databases as well. It also has good transaction, stored procedure, referential integrity and trigger support (if you're familiary with those important database features). Firebird runs on Windows, Linux and many other platforms, has PHP support for web page scripting, and requires no DBA management for small applications.
Hope this helps!