<flame> It's not nearly as easy as you're thinking </flame>
That aside (just has to be said to posts like this, not meant to be discouraging, instead meant to be informing) the best way to get started would be to get together some capital. If you are going to be offering dedicated machines you are going to need quite a bit of money to invest in the hardware alone. A full rack with power and a 100mbit feed can be had for around $1800 depending on location and if you catch it on a special or not. Add in the cost of machines (we'll say $500 for a very very low average) and consider that you are going to want to at least have maybe 20 machines ready when you launch your business of different ocnfigurations. 20 * $500 = $10,000 + the $1800 a month. Now let's assume on average these machines sell for $150 a month and you rent out all 20 out of them on opening day. $150 * 20 = $3000 a month. Take away the $1800 a month for your rack, bandwidth, and power and you're looking at $1200 a month. It will take you 9 months to break even on those machines, not to mention you are going to have to invest in more to have ready. That does not include router costs, switch costs, tech costs, etc......
Now my example is not perfect as you could get a lower commit to start out with and everything else, the point of that post is that you should really sit down and write out a full business plan for exactly what you want to do, your costs, your expected growth, etc... You can always modify your plan as you go, but at least have something to get yourself started. A better option would be looking into reselling machines for a datacenter such as LayeredTech (just my opinion of course).
Now you are talking about selling computers, the question you have to ask is why you think your computers are better than your competitiors. This is the only way you are really going to set yourself out in the market. Most gamers like to build and customize their own rigs. Even 15 year old kids know how to put a computer toegether these days. When you are talking about getting into servers and especially 1u machines, there is a lot more to it than slapping hardware together. Ask any experienced builder and they'll tell you it's easy to fry a machine with a cheap case, wrong heat sink, etc... in a 1u. Offering tech support and warrenty's is something you can do whatever way you want to. Odds are you will recieve a warent with each piece of hardware in your machine, maybe keep them on record and if there is a defective piece have the customer return it and you ship it to the company, then ship them their new piece? Tech support is completely up to you, but if you are getting into servers and you have somebody's big time machine fail at 3am, you can most likely expect a phone call.
These are just some general guidelines from how I see it, and again I am not trying to tell you to just give up before you start, but instead be prepared for what you are going into. If you have any more questions just ask