Ni hao ma ?
(Wo hen hao, ni ne?) Heiwa did it already good. I just wanted to add, that my teachers told me that you normally answer it like I just did, so that you answer the question and at the same time ask the person also how he/she feels. They told me that this is more common.
If you want to write real Chinese characters and you have Windows Vista or higher, you easily can add languages. Just take a look at the right down corner of your screen and make a right click with your mouse on the language button and go to options. There you can add new languages, including Chinese.
You also can download a chinese program to write Chinese characters, although it is not neccessary if you can write Chinese characters with Windows. Here is the link:
Wo hen hao, xie xie!
Nǐ zěnme yàng?
I see, well I couldn't know that. :) I personally searched for a solution during years desperately, until finally one Chinese teacher told me last June how to write them.
I only want to learn to speak a little bit chinese, the letter doesn't matter