Do you know if there's any problem using the PO module (I'm using PO-MOD-1.3) with PHP 5?

I had it working on my system, but it stopped functioning earlier this month. I believe that is when I upgraded from PHP 4 to 5.

What I'm seeing is, when the user fills out their PO info, clicks the Continue button to confirm the order, the following displays:
Payment Method
Purchase Order
Purchase Order
Account name:Account Number: Purchase Order Nr:

After they submit the order, the po fields in the zen_orders table do not get any data, the only related field that does get filled in is payment_method, which shows "Purchase Order".

Any ideas where to look in the po php files?

Thanks, Mike