If you are explicitly setting the extent of the coordinate system, just swap the y-values. If you are using the auto-scale routines, call the coordinate systems InvertScaleY method. Once the coordinate system is setup correctly, set the y-intercept of the x-axis, and the direction of the axis tick marks.
pTransform1.AutoScale(Dataset1, ChartObj.AUTOAXES_NEAR, ChartObj.AUTOAXES_FAR )
' Invert y-scale
pTransform1.InvertScaleY()
.
.
.
' Define x-axis
Dim xAxis1 As New TimeAxis(pTransform1)
' Make sure x-axis intercept at top
xAxis1.AxisIntercept = pTransform1.ScaleMinY
' Point tick marks up
xAxis1.AxisTickDir = ChartObj.AXIS_MAX
chartVu.AddChartObject(xAxis1)