How to preview the effect of Plugin in the original image,when the modal dialog is open?

Hi,

I am writing a plugin to Photoshop CS2, as some plugins, I want to add a “Preview” option for my model dialog. So I want to see the effect of my Plugin in the original image when my model dialog is open.

Any one know how to do that? How to see the effect in the original image, when the dialog is open?

Thank you!