You think you need MPEG2DEC3.dll but in fact what you need is DGMPGDec.dll that comes bundled inside DGMPGDec from Neuron2.
Just unpack the dll and copy/paste it to PARanoia's folder.
That is, if you did everything right and created your D2V project file using DGIndex because if you used DVD2AVI then you really need MPEG2DEC3.dll or (even better) you need to create your project file again but this time using DGIndex.
Best collection of Avisynth filters ->
http://www.avisynth.org/warpenterprises/
You will find MPEG2DEC3.dll in there but remember that I advised you to recreate your D2V using DGIndex