Solid help's on the way. {i hope}
I have to agree with Melas on this one. brwnsuga, my chief concern with a beginner starting out on a Sportster is the engine size and all that goes along with that. The bigger the engine, the harder the learning curve. Still, if you have your heart set on a Sportster (and you have a reasonable amount of self-control), you can survive the learning curve without a scratch.
Take the training course, via the MSF or the Rider's Edge. The Rider's Edge course gives you the luxury of dumping someone else's bike while you figure out the control. Don't stop there though; find an empty parking lot, grab some chalk and PRACTICE PRACTICE PRACTICE your braking skills until they become second nature. I worked with a woman who aced the MSF course, yet broke her collarbone when she locked the rear brake and low-sided her bike in a panic situation. New riders tend to rely too much on the rear brake in panic situations; practice will help you overcome that. Your braking skills are what will save you from becoming another statistic. I cannot stress this enough . . .
Buy new, if you can afford it. Harley's Sportster Buyback program is a sweet deal, if you want to trade up in the future. Plus, the new Sportsters are for all intents and purposes maintenance free, the rubber mounted engine helps tremendously on long rides and the fuel injection allows them to run perfectly in any situation.
The Sportster is really a versatile bike. It's a good canyon carver, long haul tourer, urban crawler and campsite cavorter. They've been around since the ‘50s for a reason. Don't fret too much over that first scratch; it's God's way of keeping us humble . . .