When multiple checkboxes are selected, theire sent seperated by the ';' sign (don't know the name in English (I'm Dutch)) so you can user explode() and place all ID's in an Array. then read the array
for (blah blah)
{
$Query = "Delete blah blah where field = '$ID'
Execute SQL over and over again
}
$Query = "DELETE FROM blah blah WHERE";
for (blah blah)
{
$Query .= "field = '$ID' OR";
}
Execute SQL once