iTunes unlike some other programs does not change the meta data of a file to store the ratings you give songs, instead it saves this info as a series of files usually under your My Music folder - simply make a copy of these and when you re-install them to the same location itunes will read the file and the associated ratings.

To see what will happen - make a copy of these files, then make a change in itunes, close itunes and then replace the files in My Music with the copies

When you open itunes the rating will be back to the pre-change

Note: If you wipe the drive and put these files in the My Music folder - when itunes opens for the first time it will assume all songs are there and may even show this, you will only know which ones are missing when you try and play them

If you change locations the best way is to go into Edit> Preferences > Advanced Tab

Have the first 2 check boxes - Keep folders organized and copy files, then in the top box change the location, itunes will automatically copy the files for you to the new location

if you want to achieve the conduct by the simplest way, just download the iTnes music transfer tools. it must be in your need. there is a good software to transfer iTunes music--Cucusoft iTunes Transfer (here is the download adress.)
http://www.globalshareware.com/Multimedia-Design/Media-Management/Cucusoft-iTunes-Transfer.html
or you can learn the steps of how to transfer iTunes music by this blog:www.karabb332.xanga.com