One of my pet peeves with ASP.NET e-commerce articles and complete books is that they show all about displaying content from a database and creating shopping carts - but not how to take someone's money.
Until you have a way to get paid, you're not really an e-commerce site at all... just a catalogue with some good intentions.
Anyway, fellow MVP Rick Strahl has an extensive article on Integrating Electronic Payment Processing into ASP.NET Web Applications. ( http://www.west-wind.com/presentations/aspnetecommerce/aspnetecommerce.asp )
This has the info you need to actually accept credit cards and get money into your account.
Great stuff, Rick!