hi Ulrich,
if you're using a classical type hierarchy where you've got 1 field that dictates the group node (e.g. employee) and one field that dictates the parent node (e.g. supervisor) then you need to use the hierarchylevel function in conjunction with the grouping level function and then write out string running totals based on what those values are.
have a look at the attached report...there's no instructions on the report but the report works by noting the above mentioned two values and then creating a string running total for each hierarchy level. in this case i've only done the first 2 levels, so you'll need to create an extra set of formulae.
to open the report, extract the attachment and change the .txt extension to .rpt.
also, if you need to actually use a hierarchy in cross-tabs or charts, please see my blog post here.
i hope this helps,
jamie