The MS Word spellchecker etc. is quite expensive, and hard to find. I thought http://www.lingua-uk.com/lingua.htm would sell it, but a cursory glance revealed nothing.
To install special scripts in XP, open Windows XP "Control Panel" => "Regional and Language Options" => "Languages" tab and proceed from there. Quite simple, if you’ve got the XP CD and a not too crowded hard disk. You won’t need any other SW for Chinese. Fonts are included.
For simplified, I use the MS Pinyin IME; for Taiwan MS New Phonetic IME. Settings: Simplified: Full pinyin, Incomplete input, Enable learning, Enable user…, Word, Row style. T: Intelligent IME, Enable learning/user.
It takes some experimenting… The beauty of the learning thing is that when you have written a phrase a couple of times, you may be able to enter it abbreviated, like xnkl for Happy New Year instead of xinnian kuaile. You can also, if you’re lucky, find an included application in which you can enter such shortcuts yourself. <added> Some seem to be included. Try writing rmrb[spacebar]; the IME will probably suggest the characters for Renmin Ribao as the first choice. [Enter] to accept. </added> http://www.microsoft.com/globaldev/handson/user/IME_Paper.mspx has some helpful hints on how to use CJK IME’s.
Arabic is trickier. The MS IME uses an Arabic keyboard layout. For the few words I’ve written lately, I have picked the letters one by one from the Insert Symbol box in Word. In doing this, the letters get their correct form, and despite the cursor’s place they connect in the correct direction. (You pick b. The b will be displayed as the isolated form. Pick alif. The b changes to its initial form and connects properly to the alif, making ba.)