Go to report->selection formula->GROUP and enter:
count({table.personID},{table.personID}) >= 5
... if you want to display those people with a count of 5 or more. This assumes that you don't have record inflation at the detail level. If you do, you would have to change the summary to a distinctcount of some unique ID. Also, I'm not sure what kind of summary you are using at the casetype level--sum or count--I just guessed count.
If this doesn't work quite right, then show sample data at the detail level.
-LB