The Plugin Site

Plugin Galaxy are Harald's older filters (with the small preview windows, yes?), and AFAIK aren't compatible with CS3. However, his current
PhotoWiz line of products is CS3 ready.

Yes, you can run Plugin Galaxy in Photoshop CS3 if you run Photoshop under Rosetta. To do that click on the Photoshop icon, select File > Get Info and activate the Rosetta check box.