Doors and Windows - Window replacement versus sash kit

We need to either replace or install sash kit in our wood double hung windows. House was built in 1948, and we are in a fairly mild climate. Where do you go to find a detailed step by step procedure on the above? We would start with windows in the garage to get the hang of it (no pun intended). That way if we make any mistakes, we won't be in big trouble. If we opted to have a professional replace them, how do you find a reputable contractor? My neice had Sears install vinyl and they are separating at the seams. Help!!!!!

My suggestion is to replace the old windows. Even in a "mild climate", they are costing you a lot in utilities. Shop for windows by comparing the warranties and construction, as well as the price. If your neice's vinyls are coming apart at the seams, the frames are butt jointed and held together with screws. The better vinyl's have the corners welded together, not mechanically fastened. How long of a warranty did your neice get on hers? If they are still under warranty, she should be talking long and hard with Sears about them. Find a reputable contractor by asking for references, then check them out. Also check with your State's Contractor's Licensing Board, and the Better Business Bureau.