I'm all for safety but I have to disagree with the "starter bike" recommendation for two reasons. First, the basics of biking are covered through dirt riding (balance, shifting, steering the "wrong way", looking where you want to go, emergency maneuvers, rear vs front braking, etc). Second, the basics of driving are covered through a few years of driving a car (road rules, speed limits, traffic, other drivers, etc). Starter bikes are for 18-21 year old kids who have never ridden a motorcycle before. With the skills (I assume) you already have from your experience, you'll graduate on to "normal bike" level way in less than one season. Unless you want to buy two bikes in the first year just get the bike you want and be careful. The main differences between street and dirt bikes (power and weight) are exceedingly apparent within 1min of pulling out of your driveway.
Also; Test drive test drive test drive.
Good luck!
Ps, The best piece of street riding advice I ever received came from an old man who had spent his life on harleys. It is in regard to other drivers and it is to "pretend you are invisible. Don't ever assume anyone can see you on the road because they probably can't."
Posted from my BlackBerry using BerryBlab