I would be inclined to start a new company for 2008. I would enter as much information from Dec. 31, 2007 as you have while in history mode - bank balance and outstanding receivables if that is all you have.
What you need from 2007 is a complete balance sheet to give you the opening balances for January 1, 2008.
Somewhere, somehow, somebody has filed a 2007 tax return (at least I hope so) for this client. With a little luck the tax return was done by an accountant who has working papers which should give you all the information you need.
Once you have entered all the information you are able to get, finish history and carry on. In your client notes you should have details on what you were able to get and what is missing from 2007.
You can only work with the information your client gives you.
If, at some later time you get further information from 2007 you can make a journal entry (entries ???) to enter the missing balance sheet information. As you make these entries one side will be either a dr or a cr to retained earnings.