Replacing rotted wood under siding.

Hi
I need to replace some rotting wood that I have under the siding. I was wondering if anyone could give me any advice about going about it - Like what to replace the wood with, and maybe how to treat it so that I don't have to do it again anytime soon.
Thanks

What type of wood is under the siding. Is it plywood or 1x6 or ??? What is the relative age of the house? Where is the rot? You first need to determine if the rot is caused by moisture or pests i.e. termites, carpenter ants, etc. Next determine the extent of the rot to see if the studs under the sheathing are effected. If the rot is caused by moisture you need to make sure that there are no active leaks or infiltration. If you are looking for a short answer remove the siding from around the area. Cut a square from a fresh sheet of 3/4" CDX plywood (assuming you sheathing is 3/4" thick) that is larger than the rotted area, make sure the vertical edges to the left and right overlap a stud. Place this fresh cut piece over the rotted area and outline it with a marker. Now cut out the rotted area with a circular saw (remember To set the blade depth so you don't cut through any studs). Now use some galvanized nails or deck screws and secure the new wood to the studs every 12" or so. If the sheathing is covered with Tyvek or Typar type moisture barrier replace it and secure the seams with the appropriate tape (don't just settle for duct tape). If it is black felt paper use that type to replace it. Replace the siding. If this is vinyl siding use some galvanized roofing nails to re secure it but remember don't nail the siding tight or it will buckle. Leave a dime's worth of thickness between the nail head and the siding. Any further questions just post or message.