The easiest way to transfer your itunes to another computer:
1 - sync your ipod with your current itunes, making sure you get everything on there
2- download latest itunes to your new computer from internet
3 - hook up your ipod to new computer, but choose NO when it asks if you want to sync
4 - access your ipod through your "my computer" menu, go to properites, and enable disk use
5 - go to your new itunes and choose "import library"
6 - somewhere in there (I can't remember exactly where) you will have an option to copy imported material and choose YES
Everything on your ipod will copy to your new itunes and be saved on your new hard drive. You will lose playlists, but that's it. Don't sync your ipod on your new computer until you are SURE that you have copied everything to your hard drive, b/c syncing erases what was on there before.
You can sync up to 3 or 4 computers with one ipod. Itunes will make you identify the second computer.
If you have any problems, just google "transferring itunes" or something like that. Good luck!