Topaz products crashing photoshop on an iMac

Eric;
I am having a problem with my iMac (w/4 megs and lots of scratch space) and Photoshop CS3 have not tried it on CS4 yet. But when working on a project if I try and switch from one Topaz product to another while working on the same image it crashes photoshop. This happens if I save the image before switching or not. For example if I switch from Topaz Adjust to Topaz Vivacity it crashes. As a rule my iMac hardly ever crashes.

Any ideas?

Jim Crabtree
crabtreephoto.@netscape.net