$top = 10;
$bottom = 10;
$q=mysql_query("SELECT * FROM mytable LIMIT $top,$bottom");
The $top variable is what row you want to start your selecting from. (Note, The offset of the initial row is 0, not 1)
The $bottom variable is how many rows you want to retrieve.
You might want to read the mysql manual on select more.
I'm not sure why it's sending you all 1-20 rows... maybe your database only has 20 rows of data?