Raghu,

Why would you bring in historical data into a live production system?
Is this a merger of two companies?

Then ideally you should create a separate ledger and move the data for both the companies into this new ledger.

If you really have to bring in the data into closed periods then you have two options:

1- Open periods, import journals, close periods (This will raise auditing related concerns)
2- You can simply bring in ending balances of 5 years activity into an open period of your production system. You can create one journal in GL INTERFACE table representing ending balances of last 5 years of activity.

I hope that helps.