It doesn't work with all custom roms but you can try and let us know.
If you need a full rom ready to go download the one based on Cyanogen "The big file".
Flashing Update Files
Flashing instructions for arabic update.zip
Flashing file for Nexus one (and other android devices that are Rooted and have a modified recovery ROM)
The device being modified needs to be Rooted and has a modified Recovery Image installed. See here: http://forum.xda-developers.com/showthread.php?t=619153
To begin updating, simply copy the update zip file to your sd-card. Then you will need to boot into recovery mode where you will be able to select the file to apply as an update.
After that, reboot your phone to successfully get Arabic shaping in all programs.