moving from mysql 5.0 to 5.1

Problem Statement : 386 GB of MySQL 5.0 Compressed MyISAM tables (Merge engine used)  need to be migrated to MySQL 5.1 Compressed/Partitioned tables. Also we had to add a few new columns and change the datatype of few existing columns.
Initial plan : Setup the MySQL 5.1 database with the schema with partitioning to which the [...]