Hi Geoff,
Well, I have several versions of Crystal Reports, and they all function the same way.
Create a new parameter - give it a name, and select the data type by dropping down the box and choosing a data type.
Right underneath that drop down box is a "Set Default Values" button. Press it. Voila!
You must create a new paramter through the Insert menu or the Field explorer box.
Hopes this sorts the confusion.
Cheers,
paulmarr@arcom.com.au