Welcome to Webmasterworld! Drop shipping is a great way to boost incoming capital without investing the vast sums in warehousing and shipping, I say go right ahead with that.
Shopping carts are part of any ecommerce package, and often the terms are used in place of each other. There are many platforms available to you, both pre-made and "out of the box" as you put it.
Some of the things you will need to think about before you decide on a cart:
1) Will you want to manage the hosting?
1.5) Will you want to manage your server?
2) Will you be trying to handle large or smaller volume?
3) Do you wish to use a windows/linux/bsd/OSX platform?
OScommerce offers many customizable features for smaller to mid-sized e-stores, and works with most major credit card gateways. It is up to you to customize it, but that sounds like what you are looking for.