Unfortunately, if PowerDVD lags while playing a DVD, you either have a really slow CPU, really slow GPU or really slow both. If you enable acceleration, that will definitely help.
You could try copying a DVD to your hard drive using DVD Decrypter or similar and then playing from there. This is to see if there are any problems with your DVD drive speed or settings, which I doubt.
I still recommend the same as my last post. Uninstall all codecs and codec packs such as K-Lite that you have previously installed. Then install only ffdshow.