You could copy the ARIALN.TTF font file from c:\windows\fonts on the XP machine to someplace on the 2003 machine, then go to control panel --> fonts on the 2003 machine, select file --> install new font and tell it where to find the file.
You SHOULD be able to just drop the file into c:\windows\fonts folder ont he 2003 machine, but you might as well do it through control panel.