make your select similar to this:
select * from table limit 0,20
the limit will show the first 20 entries, then if you want to show the next 20, you would limit 21,20 (21 = offset, 20 = num of rows to return) ... note: first record is 0, not 1..
check out http://www.mysql.com/doc/S/E/SELECT.html for additional info and examples..
John