DPP is not great for noise reduction (or visible noise for that matter). It tends to show more noise than other RAW converters in my opinion. Adobe Camera Raw (ACR) or Bibble are much better as a RAW converters (as far as noise is concerned). Noise Ninja and Noiseware Pro are also very good plugins that have stand alone versions (I think).
Keep in mind that it is generally not a good idea to totally eliminate the noise, the idea is to reduce some noise while retaining detail. FYI, in my opinion, ISO1250 is an excellent compromise between ISO speed and noise performance. Of course, the biggest factor in keeping noise down is proper exposure (or shooting to the right).