C# App crashes when trying to load large datatable

Hi all!

I am trying to load an *enormous* datafile into an array or some other structure to manipulate it (100 million rows, though each row only about 7 bytes in total).  I have found that XP windows freezes totally (need to hold down power button to turn it off!) when it gets to a certain size in memory.  I've had some success loading the data into 3 arrays (an int16, an int32 and a byte for each record, eg 111, 22222, 3) without it crashing.  However if I try to load the same data into a datatable, XP crashes.

I've looked at various options but am no expert.  There seem to be things like weak references, BTREE's etc that all sound too complicated.  All I really wanted was for the damn thing to be held in virtual memory and looked after transparently by the system!  I've set the virtual memory to be system managed, but it doesn't seem to max that out.  I searched out something on this site about a 1.2gig limitation per process, though I don't think I'm pushing that limit with this exercise.

SO, essentially I want my set of data to be available in a datatable, ready for me to sort/filter/manipulate using the datatable's methods.  Why doesn't windows use virtual memory rather than crashing?  What happened to the idea of 'managed code' that is meant to do the mem management for me?  

My code is below...  If you set the maxrecordstoread to 1000, it's fine of course.  If you set it to the larger number (101 million!) it crashes after 5-6 million (see that I'm writing a log file as a 'black box').  I know it's a lot of records, but a DB is too slow for my purposes (trying to analyse trends in this data).

Many thanks guys!

        private void button3_Click(object sender, EventArgs e)
        {
            // Input file data lines look like these if you are masochistic and want to generate a dummy set!:
            //1,1248029,3
            //1,1842128,4
            //1,2238063,3
            //1,1503895,4
            //1,2207774,5
            //1,2590061,3

            DataTable dt = new DataTable();
            dt.Columns.Add("movieid", typeof(Int16));
            dt.Columns.Add("user", typeof(Int32));
            dt.Columns.Add("rating", typeof(byte));

            StreamReader sr = new StreamReader(File.OpenRead(@"d://joinedout.txt"));
            string aLine;
            Int64 counter = 0;
            Int64 maxrecordstoread = 110000000;
            //Int64 maxrecordstoread = 1000;
            string[] fields;

            StreamWriter sw = new StreamWriter("d://log.txt", true);

            while (!sr.EndOfStream && counter < maxrecordstoread)
            {
                counter++;
                aLine = sr.ReadLine();
                fields = aLine.Split(',');

                dt.Rows.Add((new Object[] { Convert.ToInt16(fields[0]), Convert.ToInt32(fields[1]), Convert.ToByte(fields[2]) }));
                sw.Write(counter.ToString() + "\r\n");
            }

            label1.Text = "Loaded";

        }