how to see custom form in the reading pane?

I also put this questions on to the microsoft.public.outlook newsgroep ...

I am using custom forms for my contacts. It works fine if I am opening
contacts by dubbleclicking on the item

But if I am using the reading pane on the right or bottom I only see the
standard Outlook 2003 form (IPM.contact) instead of my custom form.

How can i make the reading pane use my custom form instead of the standard
IPM.contact form???

Any help is very appreciated!

Sabine