You can connect to the MySQL server via command line (use the mysql.exe program in your /xampp/mysql/bin).
The db.opt file is just for various database options (like characterset and collation). You did not mention any .MYD (Table Database) or .MYI (Table Index) files. Were all your table empty? If not and you do not have those files, you did not bring your actual data with you.
Assuming you are using MyISAM instead of InnoDB, it looks like it should be fairly straightforward to do the copy.
People generally do the following:
1. Stop the MySQL server
2. Copy the database folders (includes .frm, .opt, .myi, .myd files and all other files that might be in that database folder) you want from the first mysql data folder to the target mysql data folder
3. Restart the MySQL server
You may also need to try to issue a 'create database' with the database names you are copying to get them to show up. You may also need to recreate users/permissions on those databases/tables.