You can use a search engine like Google to find free word processing software and etc.
Free Arabic word processor
http://www.google.com/search?hl=en&site=&q=Free++Arabic+++word++processor+&oq=Free++Arabic+++word++processor+&aq=f&aqi=g-v7&aql=&gs_sm=13&gs_upl=2265l11984l0l13859l33l33l1l9l9l0l78l1482l23l23l0
AbiWord (Open Source - free) supports right-to-left, left-to-right, and mixed-mode text. This means that in addition to supporting European languages, AbiWord supports languages like Hebrew and Arabic as well.
http://www.abisource.com/download/
Here is a good link showing you the Arabic Keyboard Layout in Windows, plus more good stuff like how to add the fonts and Arabic Language support in Windows:
http://zsigri.tripod.com/fontboard/arabic.html
OpenOffice (open source - free) can use as long as you have the fonts/keyboard layout - see above link for more info on keyboard layouts, here to download open office
http://www.openoffice.org/download/index.html
http://www.openoffice.org/dev_docs/features/3.1/
Good luck and I hope this will help