question about BarPlot axis label values

["Kurbat, Matt" <Matt.Kurbat@kmv.com>]

Dear Splus Users,

I'm attempting to make a stacked bar plot  (my parameters: Windows NT, Splus
2000).
The bars correspond to the 6 values of a nominal categorical variable.  
Call this variable "CategoricalVariable", and call its values 'a', 'b', 'c',
'd', 'e', and 'f'. 
When I create this plot, using the code below, the values on the x-axis
under
the 6 bars are the numbers 1,2,3,4,5,6. 
I would instead *LIKE* to have the values 'a', 'b', etc. appear under bars
1-6 respectively.

Does anyone know how to do this?
I've been poring over the online help, etc., but to no avail.

Thank you,
Matt Kurbat

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My code:

guiPlot( PlotType = "Stacked Bar")
guiModify( "BarPlot", Name = "GS1$1$1",
        DataSet = "Data",
        xColumn = "CategoricalVariable",
        yColumn = "x,y",
        Crop = F,
        BarBase = "Zero",
        BarFillType = "2 Color Range",
        StartFillColor = "Black",
        EndFillColor = "Lt Gray")
guiClose("data.frame", "Data")