The group select is used to include or exclude an entire group based on the result(s) of a group summary.
It is applied after the record select.
all groups still appear in the group tree and are still included in any summarizations of the data unless exclude using varaible formula or running totals
1. you use the summarization of the group field on the group
2.If you select the summarized group value the select expert will default to using a group criteria. You can use the formual editor if you want or you can use the GUI interface in the select expert
3."entry" is the feild being summarized by the day and disk ID
All that said I do not think this process would work for a CrossTab. I believe the CT is built before the group select condition is applied. If you move away form the CT then this would likely work.
There are ways to suppress the values in the CT if they are > 95.