Most PSP plug-ins are not. If memory doesn't fail me, almost all PSP6, 7 and CS are not (if not all). PSP5.5 and 5 can be made to work in Photo-Paint just fine, almost all of them... All you've got to do is:

Copy "plugin.dll" from your Photoshop folder to "windows\system32" folder and then in CPT options indicate the folder where photoshop plugins are stored... and there you go... all the photoshop things ready for use in CPT.