Basically you just set the name of each check box to be... for instance "customer[]", which makes it into an array. Set the value of each check box to be the row number in the database table.
Once submitted you just have to loop through the posted variable as an array, ie
PHP Code:
$count = count($_POST['customer']);
for($i=0; $i < $count; $i++)
{
// do whatever to each customer id
// each is will be $_POST['customer'][$i]
}
Of course you will want to verify all posted data is safe.
If you need any more explanation I will try to go more in depth or write you an example