Crystal Reports: Multiple Value Parameter Field

I have a report that breaks the recordset up into groups and then counts the record in each group.

I want to pass a list of values into the report as a parameter, have that list broken into a multiple value parameter field and then only show the groups where the group name field only matches only of the values I passed in.

So,
Question #1: how should I pass in the list? is comma delimited the standard?

Question #2: what's the syntax for only showing groups that match one of the multiple parameter values?

Thanks in advance.
Putts