Richard and Usman,
I've got much the same question. We want to offer multiple courses for payment, and after a first pass through PayPal's settings, I'm not seeing a way to do it. We've heard of a service called CourseMerchant.com which costs about $50/month and would rather not spend the money but aren't sure if there are other options. Has either of you come to a solution yet or looked at CourseMerchant?