> So, where is the difference between using SQlite3 or MySQL?
SQLite3 is much easier to use - just make a new database in that format and off you go (though for better performance you may want to read [msg=4942]this[/msg]).
With MySQL (and other SQL varieties) you can run the database and its driver on a dedicated server, which offers better performance and security in multi-user environments, and better management of access rights (for instance, you can make certain database tables write-only for some users, e.g. to prevent that they thumbnail images from their local drives). Additionally, it's generally easier to incorporate (My)SQL type databases in other applications (such as an interactive website). It takes more effort and knowledge to set up though.