line 1095 in lib.php in assignments is a good example:
$select = 'SELECT u.id, u.id, u.firstname, u.lastname, u.picture, s.id AS submissionid, s.grade, s.submissioncomment, s.timemodified, s.timemarked, ((s.timemarked > 0) AND (s.timemarked >= s.timemodified)) AS status ';

returns no records for sql 2005
if changed to the following it works:

$select = 'SELECT u.id, u.id, u.firstname, u.lastname, u.picture, s.id AS submissionid, s.grade, s.submissioncomment, s.timemodified, s.timemarked, ';
if ($CFG->dbtype == 'mssql' || $CFG->dbtype == 'odbc_mssql' || $CFG->dbtype == 'mssql_n')

{ $select .= ' Case When ((s.timemarked > 0) AND (s.timemarked >= s.timemodified)) THEN \'True\' Else \'False\' End AS status '; }

else

{ $select .=' ((s.timemarked > 0) AND (s.timemarked >= s.timemodified)) AS status '; }