Determine AR Customer Balance - As At Point-In-Time

It definitely requires that you do it in SQL. It can be very straightforward until you get into some wacky exceptions, particularly if you use national accounts, do a lot of writeoffs, RTMs,, etc.. How familiar are you with the AR tables?

I'm not sure why you'd have to do this with SQL. AR256 ties out to a moment in time of the time (although it cannot be run by customer) and AR251 also can be run as of a date.
Granted, having used both programs to reconcile to the GL, they aren't perfect. but they are very close.
I have come close to building an AR tie out program in SQL but it's very, very complicated - partially because each transaction type really requires it's own SQL.
Question - do you just need a balance (which isn't that bad) or an actual listing of open items (more probable).

Thanks for the prompt responses - John/Adam:

A little clarification/context required on my part (sorry). I am looking for a "SQL-Based" solution here - as I am planning on creating a "By-Customer" function or view that will retrieve the balance, given the passed date parameter and will be consumed by another enterprise application. As such - the AR256 & AR251 reports are not a suitable solution (although, their underlying data retrieval logic might be).

I am pretty familiar with the AR tables - NOT using National accounts - RTM's will come into play - as will Obligation Grouping(AR44.1). For this objective - I am only interested in the balance - however - I will also be required to create a view of open items - but this will be a current view (not point-in-time).

Any starting-point queries or words of wisdom would be most welcome. Thanks for your time here guys.

If you are just creating a balance it's not so hard - assuming your history is in good shape (and depending on the volume of records).
Essentially, one can query all the valid records for the customer (AROITEMS, ARPAYMENT, aRRTM, ARADJUST) and do the math. (add your invoice, subtract your credits, adjustments and payments, add return to maker) selecting all records through a given date. Be warned - depending on how you converted your history when you started, you may have to make an exception as some people convert closed invoices without the matching payments etc.