i have seen a few forums talk about this ( all from searching google and how to repair scratched PDA screens)

some say that the use of Armor All works (but i dont know about useing it)

http://www.armorall.com/

here is another method you can try

http://www.brian-middleton.com/ipod/

he used this http://www.noscratch.com/novus/

also some forums talked about this

http://www.displex.com/

and also i have seen people talk about plexus plastic cleaner

http://www.plexusplasticcleaner.com/

and i have some mention about the lens doctor

http://lens-repair.com/

after you find something that you use to remove most of the scratches i would recommend getting a screen protector.

http://www.nushield.com/manufacturer_detail.php?apptypeid=PDA&manufacturerid=Apple+Newton

or from here

http://www.gementerprises.com/newton2.htm

or just buy a screen replacement from the above site