I am trying to build a web site for my uncle's company and he would like to have a online store. I don't know what is the best way of building a online store for him. He sells sports memorabilia, so there would be a ton of stuff to have online. You can check out the site now. I'm still working on it. http://jcsports1.com/
there are quite a few online store software kits you can buy, just do a search on google and I'm sure you'll find a fair number.
You could do it yourself, but it's a lot of work, especially if you're just starting into the whole ASP thing. You're going to have to learn a whole lot obout databases, coding, and payment provider services....I'd suggest you have a look online for ready made packages and save yourself a lot of heartache.