I have been here three weeks so i am no expert, but i had the same worries before i got here. Yes you can wear jeans... just make sure that your midriff isn't hanging out. No you do not have to cover your hair... unless you want too.
If you feel comfortable wearing something to the office (assuming you might work in a professional offic) or to a meeting with the president of your company, or on a first date where you wanted to make a really good impression of the girl you take home to mom, then it's a safe bet that you can feel free to wear it here.
Bare shoulders around town are frowned on and so are short skirts and shorts. Knee length dresses and skirts and peddle pushers are fine.
Rule of thumb...if you feel you might be showing too much... you probably are. But once you are here for a few days you will have a pretty good grasp of what is acceptible and what isn't. Truth be told... I have to go shopping... i left all my "good" stuff at home and now realize that i could have brought it to wear out.
I hope this helps.