I will explain a little more:

Access doesn't fit because he doesn't treat multiple read-write very well.
SQLite and compact SQL won't fit as well.

I can't decide between SQL Express 2005 and MySQL...
Because from one hand it's important that the installation will be fast and simple (which is the case with MySQL), from the other hand it's important to be able to program and maintain it easily and fast (which is the case with SQL Express 2005).

maybe you have a tip for me?

Or maybe I'm missing something and there is anothere DB I haven't thought about?