You could use database backup tools to export just the relevant tables, then restore into the target db. Make sure you use the relevant API views as these are designed for import/export.
If you don't want to use these tools you can export days from lists by right clicking and exporting to CSV. You can then use the xTuple supplied CSVImport application to import the CSV data back into the target db.
Make sure you test the process thoroughly first to make sure you have all the necessary fields populated. Also remember that an item also needs item site/source/tax/cost information. These must also be exported and loaded for an item to work.