hi Catherine,
you may wish to use a conditional formula as the column values instead of fields. you'd really need to give us more info on exactly what you're trying to do.
as an example, if i want to filter out columns i could create a formula like
if {Product.Product Class} = "Bicycle"
then {Product.Product Name}
and then use this formula for the columns.
now for the summary, i'd also need to create a formula like
if {Product.Product Class} = "Bicycle"
then {Orders_Detail.Quantity}
then in the cross-tab expert > Customize Style tab > choose Suppress Empty Columns.
-jamie