When moving to Tally.ERP 9 from other software (legacy) products you have two choices:
The first option is the simplest - you 'cut over' to Tally.ERP 9 by ensuring that all opening balances and open dues (bill numbers, due dates & amounts) are available; here you continue to keep your previous software only to review old transactions.
The second option ranges from simple to very complex depending on how current transactions are stored and managed – yet you may choose to go with this option for several reasons and this is fully supported.
In both cases, what is required is that data be extracted from the legacy system and be made available in a specific XML format, which is then imported by Tally.ERP 9. These formats are available from within our product itself: all that is required is that you create a master or a transaction (in Tally.ERP 9) with a sample of the data you will provide and export these. The exported XML is in the same XML format that is required for import!
As before, it is best to plan this as a structured exercise along with your chosen Tally Partner, to ensure that your business is not impacted in unplanned ways.