First, make backup files of everything! It's unlikely that anything will go catastrophically wrong during your move -- but what if it did? Simply copying your most valuable files -- family pictures, that novel in progress, your tax records -- onto a CD can save you all kinds of grief.
PCs have a utility called SHIPDISK.EXE which can "park" the heads of your hard drive to prevent problems in transit. Once you run this program, turn the computer off and unplug it from the power source. When you plug it in and turn it back on, the heads will unpark themselves.
If you have the original carton in which your PC was shipped, use it. If not, pack your PC with plenty of padding (particularly on the monitor screen) in a sturdy box.