I think a little more information is in order. What gives you an error- loading PJ64 or the plugin? Which plugin? For Rice's you need support files. For Glide 64 you need a wrapper for non-Voodoo cards (like yours).
As for which plugin is the best, that depends on your Radeon. Assuming you're talking about video plugins, if your card supports pixel shaders (8500+) Rice's is very good. GLn64 is also good for 8500+. For anything lower than 8500 Jabo's and Glide64 + Hacktarux's wrapper are what you need.