Is it possible to migrate a Trac database to Redmine if the two systems are in different machines any other way than by copying Trac to the other machine? Migration within the same box is easy: http://www.redmine.org/wiki/redmine/RedmineMigrate, but since the migration requires access to Trac files, I can't see how this could be done.
I have no experience migrating Trac to Redmine, but I do see one solution.
It's a bit out there, but:
Archive the trac directory on the first system, then move it to the new system and extract it somewhere. Then go through the migration procedure and see if it works.
If you are using a database system other sqlite and it asks you for connection details, fill out the details as if you were connecting to it externally (don't use localhost for the host)
Example:
Trac directory []: /path/to/extracted/trac
Trac database adapter (sqlite, sqlite3, mysql, postgresql) [sqlite]: mysql
Trac database host [localhost]: oldserver.example.com
Trac database port [3306]:
Trac database name []: trac_db
Trac database schema [public]:
Trac database username []: trac_db_username
Trac database password []: trac_db_password
Database encoding [UTF-8]:
Target project identifier []: myproject
Again, this probably won't work, but it's worth a try.