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Yes, Pro Logic II will do its best to attempt positional audio and simulate a 5.1 surround experience from only 2.0 channels. I'm not an expert in this, so I don't know for sure how the algorithm works, but this is my best guess (as a computer science major).

Think about your two ears. Note how with only two ears you can hear sounds from all directions and position them with great accuracy. Now imagine your ears were replaced with two microphones (or a stereo microphone) on set at the film studio. Those two microphones are picking up the same auditory information your ears would pick-up if you were in their place.

Now realize that it is your brain which interprets the auditory information your ears receive and assigns direction and distance to each sound. Dolby Pro Logic II is basically the brain in this analogy, and using a stereo audio source it analyzes the audio in much the same way your brain does to try and determine the position of each sound. It then separates the audio into 5 different directional channels based on the best educated guess of where the sound is originating from in the film/show.

So the question remains... how exactly does the brain determine position? Well the primary way to do this is to look at the micro-delay between the time a sound arrives at one ear compared to the other. Since sound travels relatively slowly compared to light, we are actually able to measure the time it takes for the same sound to reach one ear versus the other to determine its most likely origin.

The other key factor involved is amplitude/volume of the sound. Obviously if a particular sound is much louder in one ear than the other, it probably means it originates from that side of our head (assuming our ears are both fully functional). If we hear the same sound, but just a bit louder on one side than the other, we can get an idea of where the sound is relative to us by measuring the difference in volume as it is received at each ear.

It's possible the logic processor will also look at audio frequencies to determine which audio channel it should use. For example, the assumption may be that voices should come from the front channels while other sounds and ambient noise should go to the surround channels. To do this, the logic processor might filter different frequencies so that sounds that lie in range of the human voice tend towards the front channels, and sounds outside of that range (e.g. crowd roaring, rain drizzling) tend toward the back channels.

There are also other positioning cues which can be used to get an idea of where a particular sound is coming from. The logic processor analyzes the stereo audio and uses these cues to guess the most likely position of each sound and recreates that environment as best as possible.

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Also, I should mention that there is technical documentation available for content producers which describes in detail how to encode sound for your content so that Dolby Pro Logic II is better able to analyze and decode the sound into discrete audio channels. The logic processor should still be able to work with audio that is not specially encoded this way.

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