I think chatting is the best way of learning writing If you want to learn how you can use Appropriate sentences thats good to chat with any one is persian.

Put window CD into your computer. Open control panel window. Click on "Regional and language options". Go to the second tab named "languages". Tick the option of "Install files for complex script and right-to-left languages (including Thai)". Then press OK and wait for installing. (This needs windows CD). After that you can find "Farsi" in the list to add to your keyboard. If you have problem yet, I will be at your service.

there is a simple way. you can write Persian using Latin alphabet and this website will change it to Arabic (Persian) alphabet. http://www.behnevis.com/en/index.html

Please see the link http://www.google.com/transliterate/persian you can write Farsi in English alphabet then it will change to Farsi then copy it whatever you want. try it. for example write the salam and press space key the you see سلام

in windows is like here: http://alefba.us/how-to/add-arabic-persian-windows/