I did this in college. Unfortunately, it was a lot more profitable back then.
You need to get a business license and avoid sales tax when you buy parts. But, you will have to pay taxes when you sell.
Call a bunch of places and see if they will sell to you (a reseller) in bulk. The operating system is going to be the biggest issue. Unless you include Linux or 2nd hand copies of the OS you will not be able to charge enough money to compete with the companies that offer warranties. For the same price that you would charge to turn a profit, they can get a new name brand PC with the newest version of Windows, and a warranty they can believe in. You are going to have to convince people you will be around for 5 years, so they know you won't be a bad investment. Your competitors have ~4% markup and 24/7 tech support.
Craigslist and other classifieds would be your best bet though. Frugal, skeptical shoppers browse there first. A lot of people would rather deal with you than Best Buy any day.
This post has been edited by throwingks: Jun 6 2009, 05:51 PM