PR and the Alternative Vote

The above video appears in this explanation of the Alternative Vote system which appeared in the blog of the New York Times, linked here.

Cameron's sudden dash to Scotland and the reported concessions he has made to that already over-coddled portion of the UK and the abandonment of tried and tested Conservative principles by the Cameron Faux Tory Party during the campaign is beginning to dash earlier expectations that the Coalition Government will best solve the deficit problems and deserve some longevity by holding the centre ground.

How can other smaller parties that have previously also suffered under the First Past the Post voting system now maximize their votes assuming a shift to the Alternative Vote system and the now almost certain ongoing disgust across the country with all three of the established main parties.