I have only made vinegar from apples, but I'm sure the process would be the same with pears. You want to start with juice from the pears--we get it straight from the cider press, but you could probably also just juice them in a juicer. As long as they are not sprayed, there is no need to wash them, as you want the ambient yeasts on their skins to start you off. Basically, you want to make hard cider by letting the juice ferment in a bottle with an airlock (pour juice in bottle, cap with airlock--add nothing!). Once you have your hard cider (the airlock will stop bubbling), you can add a mother and make vinegar. You can use the cloudy part from the bottom of a bottle of Bragg's or any unfiltered and unpasteurized cider vinegar you get at a health food store (along with about a cup of the vinegar as well for each gallon of cider). You can put it in another bottle with an airlock or just put some cheesecloth (or even a piece of paper towel) over the mouth with a rubber band. Then, wait. Sniff and taste every once in a while, but it shouldn't take more than a couple of weeks, depending on the temperature. If you do a few jugs (I reuse half and gallon beer growlers), you will get a nice strong mother in each and you can just keep adding new cider to the jugs with the mothers once they get low.
Oh, and you definitely don't need to pasteurize it.
Good luck and have fun!