Looking on the Toshiba site the difference seems to be a slightly different processor Pentium® M processor Ultra Low Voltage 753 for the PPR20E and Pentium® M processor Ultra Low Voltage 773 for the PPR21E. Also the spec says the PPR21E supports wireless a/b/g whereas the PPR20E only supports b/g
Looking on the Toshiba site the difference seems to be a slightly different processor Pentium® M processor Ultra Low Voltage 753 for the PPR20E and Pentium® M processor Ultra Low Voltage 773 for the PPR21E. Also the spec says the PPR21E supports wireless a/b/g whereas the PPR20E only supports b/g