I've done this at least half a dozen times.
Open Explorer and go to the My Documents folder. In that folder is another folder called My Music. In that folder is a folder called iTunes. This is the folder you want to move. Depending on the size of the folder, several options are available. Copy to CD or DVD, USB flash drive, or network the PCs and copy the folder. I find the easiest way is to use a large flash drive as the folder must be moved in one piece. It also depends on the size of the iTunes folder.
Anyway, copy that entire folder to the new PC and put it in the same place. Then install iTunes. iTunes will find the folder where it expects to and will then log all your music.
I just bought a new laptop, a Dell Inspiron w/ Windows Vista. The old laptop (HP w/ windows XP) is slowly dying and I'm trying to get everything off of it before it completely crashes. The hardest part is iTunes. I have no idea what to do. I want to move everything in my iTunes to the new laptop. I have an iPhone, not an iPod, that I use iTunes for. I don't even know where to start. In addition to moving the library, which is what most articles seem to be about, do my actual playlists get transferred? Somebody please help me!!!