Here is the sample code for logrithm on x axis
Dim axisID As VtChAxisId
MSChart1.chartType = VtChChartType2dLine
For axisID = VtChAxisIdX To VtChAxisIdY
With MSChart1.Plot.Axis(axisID).AxisScale
.Type = VtChScaleTypeLogarithmic
.LogBase = 10
End With
Next