backup partial tables

Hi

I have an aplication (C# ) that creates lots os records with blobs (about
1Gb/month)

I want to make a backup with the older records and delete it from the main
table.
It may be necessary to restore any old data, so I need to backup before
delete.
I decided to do this: (just the important part)

//create a new table with the same structure and name like the name_date
sqlText =" CREATE TABLE myTable_" + date + " ( Id int(6) unsigned NOT NULL
..... , PRIMARY KEY (Id)) ENGINE=MyISAM;";
cmd.CommandText=sqlText;
cmd.ExecuteNonQuery();

//read data
sqlText = "SELECT * FROM myTable WHERE date_i BETWEEN '" + dateMin + "' AND
'" + dateMax +"'";
cmd.CommandText=sqlText:
dr = cmd.ExecuteReader();
while (dr.Read())
{
id_def=Convert.ToUInt32(dr["id"].ToString());
(...)
//insert the data in the new table (have to use another command and
another connection)
sqlTextInsert="INSERT INTO myTable_" + date + " (id,...) VALUES (" +
id_def + ","+...+ "')";
cmd_insert.CommandText=sqlTextInsert;
cmd_insert.ExecuteNonQuery();
}

//Delete backuped data
sqlText =" Delete * from myTable WHERE date_i BETWEEN '" + dateMin + "' AND
'" + dateMax +"'";
cmd.CommandText=sqlText;
cmd.ExecuteNonQuery();

//copy the files for network or DVD or whatever
System.IO.File.Move(bdFolder + "\\myTable_" + date + ".MYD" ,backupFolder +
"\\myTable.MYD");
System.IO.File.Move(bdFolder + "\\myTable_" + date + ".MYI" , backupFolder +
"\\myTable.MYI");
System.IO.File.Move(bdFolder + "\\myTable_" + date + ".FRM" ,backupFolder +
"\\myTable.FRM" );

This don't work because as it reads records it uses memory and memory and it
hangs.
So I changed the program to read just 1000 records in each DataReader, but
even like that it takes about 1,5 minute for each 1.000 records and I have
about 200.000 records / month so it works, but it takes lots of time.

For me it's obvious that make one insert at a time is not a good solution,
but what to do ?
I thought in copy the intire file and the delete in each table the records
that I don't want (new ones in the backup table and old ones in the
'production' table), but I also don't like this aproach.

Any idea is welcome.
Thanks
Ventura