Hi,

I have about 25000 tracks in my collection.

What database would you recommend that I use - sqllite, mysql, postgres?
Please note that I currently have no need for a database so if I install mysql or postgres it would only be for use with amarok.

use postgres. mysql is just one step above a flat file. it will make a difference as your collection grows.

^^ I wouldnt say MySQL is one step above flat file.

LOL.

MySQL is great to use - it can easily handle + 100,000 entries without any extra effort...

And what do I have to do to set up MySQL for amaroK? Is there a How-To for newbies?

Postgres handles acid properties better than mysql (even when using innodb) but that's not important here i think.
And you can find both howtos on the amarok wiki:
http://amarok.kde.org/amarokwiki/index.php/Postgresql_HowTo
http://amarok.kde.org/amarokwiki/index.php/MySQL_HowTo
and both should handle this amount of data without any problems.