Opening balances are those amounts belonging to your business due to operations prior to using Sage 50.  Because you are entering opening balances, there was activity in the company prior to the date you decided to start Sage 50.

Accounts Payable on the balance sheet is the total of all invoices owing (not yet paid) to vendors.  Therefore you should have a list of invoices not yet paid.

Accounts Receivable on the balance sheet is the total of all invoices owing (not yet paid) by customers.  Therefore you should have a list of invoices not yet paid.

Normally you would create a vendor or customer, go to the History tab of that company/person's ledger and enter the amount owing.  The total of all of them should add up to the balance sheet amount for each category.  Once these totals balance with the balance sheet you will be able to exit history mode.

By entering each individual invoice, you will then be able to properly record the payment for each individual invoice as it happens after starting to use Sage 50.

Sometimes accountants will include Accrued Liabilities with Accounts Payable on their Trial Balances so you should discuss the breakdown of these numbers with the accountant if you can't validate the total.

Don't forget to use the Maintenance, Check Data Integrity option to make sure you are balanced in all linked areas.

They are not going to give me the breakdown or the vendor info, they just want it done and say that it isn't difficult, just do it. 

Will it work if I create Supplier X or Customer Z and enter an historical invoice that matches the amount in the Accounts Payable and Accounts Receivable or will that increase the amount in those ledger accounts by doubling it?

I am in another one the companies they had me create and this is what I get when trying to move into the new fiscal year.

Checking Clients...
The sum of your Clients' information does not equal the current balance of account 2460 Accrued Liabilities.

$0.00 Total Deposit and Prepaid Order
$2,500.00 Current Balance of 2460 Accrued Liabilities
_______________
-$2,500.00 Difference

Either your Clients' historical information or the opening balance of account 2460 Accrued Liabilities, or both, is incorrect.

How would I match this one?  Make an entry that posts in Deposit & Prepaid Order?

Because it does not seem like you think there is any amounts owing to vendors as of the day before your started using Sage 50 nor any customers who owe you any money on the same date, I would not create fake customers and vendors.  Stick to reality.

I would enter the opening balance for Accounts Payable to Accrued Liabilities and the amount for Accounts Receivable to (possibly) a new account for Other Receivables.

Then because they are not linked to the subjournals, there will be no need to match them and your data integrity will match.  The accountant can deal with the amount at the end of the year.

I think by default the program uses the 2460 Prepaid Sales/Deposits account to be linked to the A/R module, not Accrued Liabilities (A/L), so maybe someone changed the name instead of creating a new A/L account.  I would check your Linked accounts under Setup, Settings, Receivables, Linked Accounts to make sure they are linked properly.