Yes this topic has been discussed several times. Go to Accounting Options, query your ledger and create a dummy legal entity and operating unit.
Create a legal entity using the second tab and attach it to your ledgerusing the first tab. Just put any address and business numbers. Dont worry about assigning balancing segment values to your legal entity. Then create one operating unit through Accounting Options as well (This option will be avaialble once you create a legal entity and attach it to your ledger). If you want to create proper legal entity and operating units then it would not hurt going through the AP sessions.