1) Rack on top of sanatized fruit in secondary. The sugar in the fruit will start a new fermentation. About 7-14 days in secondary will complete this fermentation and impart the fruit flavor.
2) The easiest thing to do is buy the pre-packaged fruit purees. These are already sanatized and ready to use. Most of the online HBSs and your LHBS should have them. Vitner's Harvest is the brand name that makes sanitary purees specifically for brewing and winemaking.
Canned would already be sanitary as well (pastuerized), but you'd need to puree them. Sanatize your blender/food processor container and puree them before adding to secondary.
Fresh produce is a bit trickier. Fresh produce has the possibility of housing wild yeast, which will turn your brew into a sour. Some fruits can be adaquately sanatized by freezing, some require pastuerizing (i.e., 160F+ water bath for about 2-3 min).
For the peaches, I'd go with the 165F water bath for about 2-3 min, then puree them in a sanatized blender/processor, then add to secondary and rack your beer on top.
Also, FYI, I've done a peach batch before myself, and it takes about 6lbs of peach per 5 gallon batch to get a noticable result.