I would second SueZQ's thoughts on an MSF (motorcycle safety foundation) course, and I would take this course before buying anything. The course insturctors provide bikes, so you don't need your own. It's offered at alot of community colleges, at least around where I live. It will give you and edge on the street, and I find it is easier to learn from an instructor I don't know that to try to learn from a close friend or family member (emotions can get in the way with folks you're close with, both on the side of the student and the teacher). Completing the MSF course, which is usually two or three days on a weekend, also counts as automatic credit towards getting your motorcycle endorsment on your license in most states. That means you would not have to take the DMV couse.
Some people are going to advise you to buy a bike you won't out grow as your skill level progresses, but I feel that a new rider starting out on some 600-700 pound beast with way more power than you are ready for is probably not a great idea. I'd stay in the 500-600cc class, or get an 883 Sportster if looking at a Harley-Davidson. Something with fairly low weight, enough power to be fun but not scary, and a seat height low enough to allow you to put both feet down at a stop is what I would recommend anyone starting out in motorcycling, male or female. I started out on a sub 600cc Honda Shadow VLX cruiser 14 years ago, then moved up to a 750cc naked bike (sort of a rice rocket with no plastic hiding the motor and no windshield), then an even more powerful 900 cc naked bike, and now I ride a Suzuki V-Strom 650 adventure bike (bike that is good mostly on pavement, but can handle some dirt riding).
How far, where, and on what type of roads you want to ride will have significant influence on what type of bike would be best for you. Here's a breakdown:
Want to ride fast on curvy, tight roads? Get a sport bike, but keep in mind that alot of these bikes aren't comfortable for long, all day rides. And some of them have fairly high seat heights and lots of horsepower.
Want to just cruise the highway and take your time down a back road? Get a cruiser, but some of these bikes will drag hard parts if you lean them too far while riding quickly through the curves. Take it easy.
Want the ability to handle any pavement and some dirt? Get an adventure or dual sport bike, but these typically have a high seat height, dirt road riding ain't easy, and your cruiser friends won't follow you on dirt.
Like the power and speed of a sport bike, but want more comfort? Get a naked bike, but these also usually have a fairly high seat height.
Want to pack your stuff and hit the interstate for a few days and lots of miles? Get a bagger or touring bike with hard luggage or saddlebags and windshield, but these can be heavy and a little over-kill for short, in-town riding.
I've had the pleasure and blessing of enjoying motorcycling for nearly 15 years, and I've put six thousand miles on my latest bike in the last eight months. I've never laid one down, but I've come pretty close too many times. It's scary sometimes, but aren't alot of fun things? My dad is closing in on 60 years old, has owned eight bikes in his lifetime. He's put tons of miles on stuff, had a few nasty wrecks, taught me how to ride (with some yelling and hurt feelings; take that MSF course!), helped me buy my first bike, still rides, and is my favorite riding partner. He told me "Motorcycles might be the death of me, but I sure do enjoy them, and I'm going to keep on riding." Put alot of thought into what bike you want. Go to some dealers and sit on some bikes. Ask questions. Never stop trying to sharpen your skills. Get some riding gear. A full face helmet, jacket, gloves and boots ain't comfortable, but dress for the crash, not the ride. Have fun and be safe. And, on a personal note, I think chicks who ride solo are hot, hot, hot!
These are 450s 
