Assuming you did something like
$key = $_POST[...];
the SQL looks fine.
Try something like this:
mysql_connect ('localhost', 'username', 'password') or die ('I cannot connect to the database. Make sure that mysql is installed and that you are trying to log in as a valid user.');
mysql_select_db ('database_name') or die ('The database specified in database_name must exist and must be accessible by the user specified in mysql_connect');
$query = "SELECT * FROM pages WHERE body LIKE '%$key%'";
$query_result_handle = mysql_query ($query) or die ('The query failed! table_name must be a valid table name that exists in the database specified in mysql_select_db');
$num_of_rows = mysql_num_rows ($query_result_handle) or die ("The query: '$query' did not return any data");
print "The query: '$query' returned $num_of_rows rows of data.
That'll tell you if you're getting any results back. From there you can do something like
while($row = mysql_fetch_row($query_result_handle))
{ .... }
To get to all the results.