private String strSqlRankName = @"Select t2.Rank From Ranks As t2, Main As t1 
					Where t1.Name=? And t1.RanID=t2.RankID";

cmd.Parameters.Add(@t1.Name,OleDbType.BSTR);

cmd.Parameters.Add("t1.Name",OleDbType.BSTR);
cmd.Parameters[ 0 ].Value=slName;
OleDbDataReader rdr = cmd.ExecuteReader();

private String strSqlRankName = @"Select t2.Rank From Ranks As t2, Main As t1 
					Where t1.Name=? And t1.RankID=t2.RankID";
.
.
String slName=listBox1.SelectedItem.ToString();
Globals.cn.Open();
OleDbCommand cmd = new OleDbCommand(strSqlRankName, Globals.cn);
cmd.Parameters.Clear();
cmd.Parameters.Add("t1.Name",OleDbType.BSTR);
cmd.Parameters[ 0 ].Value=slName;
OleDbDataReader rdr = cmd.ExecuteReader();
comboRank.Items.Clear();
comboRank.Items.Add("(не выбрано)");
while (rdr.Read())
{
	comboCompany.Items.Add(rdr[ 0 ]);
}
rdr.Close();