Here's one way of going about it:

 public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();

            var testData = 
                new TestSimpleDataPointCollection();

            chart.BindTimeSeriesCollection(
                TimeSeriesData.ToTimeSeriesCollection(
                testData));
        }
    }

    public static class Extensions
    {
        public static void BindTimeSeriesCollection(this XamDataChart chart, TimeSeriesCollection coll)
        {
            if (coll.Count < 1)
            {
                return;
            }
            var xAxis = new CategoryDateTimeXAxis();
            xAxis.ItemsSource = coll[0];
            xAxis.DateTimeMemberPath = "Time";
            xAxis.Label = "{Time}";

            var yAxis = new NumericYAxis();

            chart.Axes.Clear();
            chart.Axes.Add(xAxis);
            chart.Axes.Add(yAxis);

            chart.Series.Clear();
            foreach (var data in coll)
            {
                var line = new LineSeries();
                line.ItemsSource = data;
                line.ValueMemberPath = "Value";
                line.XAxis = xAxis;
                line.YAxis = yAxis;

                chart.Series.Add(line);
            }
        }
    }

    public class TimeSeriesCollection
        : ObservableCollection<TimeSeriesData>
    {
    }

    public class TimeSeriesData
        : ObservableCollection<TimeSeriesDataItem>
    {
        public static TimeSeriesCollection ToTimeSeriesCollection(List<SimpleDataPoint> simplePoints)
        {
            int count = SimpleDataPoint.Count;
            var coll = new TimeSeriesCollection();
            for (int i = 0; i < count; i++)
            {
                coll.Add(new TimeSeriesData());
            }

            foreach (var point in simplePoints)
            {
                for (int i = 0; i < count; i++)
                {
                    coll[i].Add(
                        new TimeSeriesDataItem()
                        {
                            Time = point.xAxis,
                            Value = point.yAxis[i]
                        });
                }
            }

            return coll;
        }
    }

    public class TimeSeriesDataItem
    {
        public DateTime Time { get; set; }
        public double Value { get; set; }
    }

    public class SimpleDataPoint
    {
        public static int Count = 4; //Some restiction
        public DateTime xAxis { get; set; }
        public float[] yAxis { get; set; }
    }

    public class TestSimpleDataPointCollection
        : List<SimpleDataPoint>
    {
        public TestSimpleDataPointCollection()
        {
            for (int i = 0; i < 20; i++)
            {
                Add(new SimpleDataPoint()
                {
                    xAxis = 
                    DateTime.Now.AddDays(i * -1),
                    yAxis = new float[] 
                    { 
                        i, 
                        i + 1, 
                        i + 2, 
                        i + 3 
                    }
                });
            }
        }
    }

Let me know if this helps.

-Graham

By That way I cannot create dynamic number of chart lines. What do I have do to a feature request?