It seems you need to get a older version of the Nvidia plug-in; the one on Nvidia's site is too recent. From Corel's knowledge base: "Paint Shop Pro supports the Adobe PhotoShop 5 plugin specification. Any plugin filter made with this specification should function fine with Paint Shop Pro products. If the plugin was made with a later PhotoShop plugin specification, then it may not function with Paint Shop Pro products."
For use with PSP9 I dowloaded version 1, 0, 0, 1 of the "dds.8bi" here:
http://www.bhmotorsports.com/download/3897. I have, however, not been able to find a similar older version of the "NormalMapFilter.8bf".
One other thing, though: it may not work if you put it in a sub-folder within the plugin-folder, even if you check the "use subfolder" option within the preferecenses/file location dialogue. Put it directly into the plugin-folder.
Peter