PivotChart Category(x Axis) As Variable

Hi all, I want to create a pivotchart from a query, embed it in a form and use a combobox in the main form to allow the user to select the x axis value. So in a query with fields city, state, country, etc the user would be able to chose one of those fields as the category(x axis across the bottom) to display data. Is this even possible? If it is, how do I do it? As it is now I can add multiple categories to my chart- but it just makes a big mess of the chart. I can embed a chart in a form and use a combobox- but it allows me to choose from within a field- but not from among fields. Also- how do I access the code to manipulate the chart? Thanx in advance