There are two strategies in migrating your books to between accounting solutions in general:
The general approach is to migrate invoices first, creating them as they exist in the current accounting solution. Then, differences with the intended balance can be calculated and the remainder posted at-once. For more comprehensive explanation see How do I migrate my existing books to LedgerSMB?
The current stable release line is 1.8. For more information about older versions, see the FAQ item about supported releases. Versions 1.2 and older should no longer be used due to known security issues that cannot be resolved in that code base.