Is there any way to custom configure your keyboard?

I don't know anything about customizing regular keys (without command, etc). But there are three different Arabic keyboard layouts. Go to System Preferences-International-Input Menu. Check the different Arabic choices, and check "show input menu in menu bar," and you can choose the different options from the menu bar. Maybe one of them is the layout you are used to. (I'm using Leopard, but it worked the same in Tiger, and I'm just assuming the three choices for Arabic are in Tiger also). If you leave the choices in the menu bar, you can then go back and forth between what's on your keyboard and the other options.

 

Try Ukelele. You can literally change any key to whatever you want. I don't have the link for it right now, so you'll have to google it.

HTH