Need to get 0B/27.2MB of archives.
After this operation, 88.1MB of additional disk space will be used.
Preconfiguring packages ...
(Reading database ... 126901 files and directories currently installed.)
Unpacking mysql-server-5.0 (from .../mysql-server-5.0_5.1.30really-5.0.77-d8-ourdelta54_i386.deb) ...
Aborting downgrade from (at least) 5.1 to 5.0.
dpkg: error processing /var/cache/apt/archives/mysql-server-5.0_5.1.30really-5.0.77-d8-ourdelta54_i386.deb (--unpack):
 subprocess pre-installation script returned error exit status 1
Errors were encountered while processing:
 /var/cache/apt/archives/mysql-server-5.0_5.1.30really-5.0.77-d8-ourdelta54_i386.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

/var/lib/dpkg/info  $ ls mysql-*
mysql-client-5.0.list     mysql-client-5.1.list    mysql-common.conffiles  mysql-common.md5sums  mysql-common.preinst   mysql-server-5.1.postrm
mysql-client-5.0.md5sums  mysql-client-5.1.postrm  mysql-common.list       mysql-common.postrm   mysql-server-5.1.list