From Karl Irvin, CPA:
The Data Transfer Utility allows QuickBooks users to quickly and easily transfer list and transaction data (invoices, bills, estimates etc.) from one QuickBooks file to another QuickBooks file. Using simple parameters, the Transfer Utility automatically makes the transfer while allowing you to control the process. QuickBooks files are opened and closed by the Transfer Utility and the regular QuickBooks program does not have to be running. Small transfers can be made in less than a minute. The utility will merge data from one QuickBooks file into another QuickBooks file without erasing or overwriting existing data.