Photoshop, Leopard and Plug-ins...

Photoshop and Leopard do not mix, especially if you have an Intel-based Mac. Either you are using a version earlier than CS3 and it is no longer compatible (or no longer supported by Adobe), or you upgraded to CS3 and most of your old plug-ins do not work anymore (apart from a few plug-ins maintained by their respective publishers). If you have this plug-in problem, for example, and you can no longer use the TWAIN plug-in for your scanner, or KPT effects, you should know that there is a solution, published by Adobe on their database.
Just check the "Open with Rosetta" box in Photoshop CS3's "Get Info" window to restore use of most of the former plug-ins, including those not written for PowerPC. The loss of speed is negligible (aside from the application's load time) as long as you do not work on images of very large size.
This work-around was suggested in the MacBidouille forum (French) regarding scanners, but the fact that old plug-ins function like new needed to be restated!