Amplifying, or attenuating only part of an Audio Stream is not all that easy. You can often get what you want, or nearly so, by using EQ to amplify part of the frequency specturm, while attenuating other frequencies. This takes so experimentation, and also critical listening.
One can gate certain frequencies, around those of the dialog, with Cutoff Filters, say both a Highpass and Lowpass Filter, setting those as needed, and again, by listening critically.
While PrE offers some Audio editing capabilities, I find much of such work better done in an audio-editing program, like Adobe Audition (my first choice), or even the free Audacity.
PS - some of the techniques that I use, are listed in this article on attempting to remove "noise" from an Audio Stream: http://forums.adobe.com/message/2860521#2860521