[Problem]
I tried to apt-get install mysql-server-5.0 mysql-client-5.0 , but the standard repository did not have it.
[Solution]
Open your /etc/apt/sources.lst file, and drop your repository links there. Here is a nice one, where you also will find a MySQL5 server and client package.
deb http://dotdeb.pimpmylinux.org/ stable all
deb-src http://dotdeb.pimpmylinux.org/ stable all