N00b!

all bikes really depend on where you are riding
your best bet for a good first bike, would be a 200-230.
very first bike was a 1978 yamaha IT175. great bike with plenty of power and will get you where ever you need to go.

also, this is my personal opinion, for a first bike try to get a four stroke. and if you enjoy it enough and want more power and what not, then get a 2 stroke (smoker)

is where you will be riding open area or tight trails?

Okay floopy here's the rundown. Given the fact that you are a short, lightweight, that doesn't ride here is a list of bikes from every brand that would fit you physically, and fit your riding style (probably slow) Haha. Starting with Honda. CRF 230. Great bike, E-start low seat height, can actually pull its weight around. XR 250. also a great bike. You might be on tippy toes for that one but you'll learn not to fall over; always a great ability. Kawasaki: KLX 300. this bike is a favorite among shorties. Just be careful about riding it. Its pretty fast. But don't let that scare you. Just use less throttle. Also the predicesor to the 300. The KLX 250. same bike little bit less power. Kind of hard to find though. Suzuki: DRZ 250. Ride this bike for a little while then get rid of it. It's great to learn on but you'll get sick of it quick. DR 350. I owned one of these and they are great. That bike was my big transition from sucky rider to good rider. This is a little bit bigger bike too like the XR 250. Yamaha: TTR-250. This is a great bike for a bigginer. It's a big bike too but I was riding bikes bigger than these when I was 12 years old so don't let that shake you off. You can always shave the seat too. These bikes are all considered low tech and easy to work on and they have bullet proof motors. The KLX 300 is the most powerful and least is the CRF 230. Okay as far as your other questions; The difference between two strokes and 4 strokes. 4 strokes have more torque, acclerate quicker (at least the race bikes do), and are easier to maintain. Just put gas in it and change the oil when your supposed to.But when they break they are more expensive to fix. These bikes that I meantioned will hardly break as long as you maintain them correctly. 2 strokes have great low end power and are a whole lot of fun. But they take a little more attention as far as attention. You have to mix the gas and you're not supposed to run it out of gas as it can possibly fry your top end. They are also easy to fix though. A big engine fix can be about $250 and consist of 20 part as compared to $600 and have a billion parts like a 4 stroke. The only reason I didnt meantion any in my list of bikes is because all the 2-strokes nowadays are full blown race bike. Not so great for beginners. KTM makes great 2 strokes but every KTM you buy will scare you except the 50. That's why KTM's bikes aren't meantioned either. If you want to know about Acronyms look at Motospeak on this site.

well put rostifer

well floppy, what do you think?

you had stated that you had trails and wooded areas?
wooded areas are really tight with not much room to work. unless you know your bike and you are extremely comfortable with it, stay away.

I have a 2003 XR250R i am going to sell for 2,000, it was my first bike.

good rule for buying the bike is to look over it, i know it sounds like a dad talking but its for real. you want to look at your rear fender to see rubber marks(meaning its been bottomed out) ask about any recent work done to it. ask how it was ridden *raced, trails, hard riding* has the oil been changed every 2 rides if ridden normal. ever been wrecked. ask them to start the bike. first 3 kicks is perfect. more than 10 might need to do some deep cleaning and check the carb. check the tires. and the over all condition of the bike. for your first bike you really dont want to hassle with a fixer upper.
thats my personal opinon btw, sometimes you get lucky but sometimes you get screwed