My question: can someone point me to the specific steps I need to go through to allow my client to do online credit-card processing without going through a Yahoo Merchant account (or similar)?

I'm also open to recommendations.

Boring details: I have clients that are ready to do online credit-card processing for conference registrations. I already have my custom application that collects all of the info I need, including the credit card info. I am comfortable with SSL and basic programming in ASP.

Because of the customized nature of the info (hotel reservations, etc.) and the back-end admin, I really want to use my program - my fear is that if I go through a yahoo merchant account, I can take them up through the registration, write this info to the db, then send them to payment but...then someone could register but skip paying.

Thank you!