I have just been setting up an osCommerce website to use Paypal's IPN as the payment method to accept credit card and paypal payments. I downloaded the official osCommerce Paypal IPN module from the contributions site, because the one that comes with 2.2MS2 is out of date.

After downloading this and installing it, I made a test order on the osCommerce store, and when I was directed to Paypal the amount to pay was $0.00 USD. As this is an Australian site, dealing in Australian currency (AUD) only, there were 2 problems. The zero order amount, and the fact that it was in USD.