copying my itunes library from my old computer to the new one

Copy the entire iTunes folder (My documents/My Music/iTunes) from the old drive to the new drive.

If the songs are on your iPod there are a number of third party utilities that you can use to retrieve the music files and playlists from it. You'll find that they have varying degrees of functionality and some will transfer movies, videos, photos, podcasts and games as well. Have a look at the web pages and documentation, this is just a small selection of what's available, they are generally quite straightforward. You can read reviews and comparisons of some of them here:
Wired News - Rescue Your Stranded Tunes
Comparison of iPod managers

TuneJack Windows Only
iPod2PC Windows Only
iGadget Windows Only
iDump Windows Only
SharePod Windows Only
iPodRip Mac & Windows
YamiPod Mac and Windows
Music Rescue Mac & Windows
iPodCopy Mac and Windows
iRepo Mac & Windows (iPhone and iPod Touch compatible)
iPod Access Mac & Windows (iPhone and iPod Touch compatible)

If you have any iTunes Music Store purchases the transfer of purchased content from the iPod to authorised computers was introduced with iTunes 7. You'll find details in this article: Copying iTunes Store purchases from your iPod or iPhone to a computer

There's also a manual method of copying songs from your iPod to a Mac or PC. The procedure is a bit involved and won't recover playlists but if you're interested it's available on page 2 at this link: Copying Content from your iPod to your Computer - The Definitive Guide

Start iTunes hiolding the Shift key.
Select *Choose existing library* and select the iTunes library file in the iTunes folder you copied over.

Try this! It should work for you.

http://docs.info.apple.com/article.html?artnum=300173

Make sure you are selecting the same file you copied over.
If it's the same file, it will be the same as on the old computer.

Since I can't open my old iTunes (some xp --> vista problem) I can't "pack" or "move" anything.

You don't need iTunes to copy files.

How did you copy the iTunes folder from the old computer?

I fixed an IDE-to-USB cable and connected the old harddisk to the new notebook. So everything is there - but I still can't copy the whole library with playlists and all

So you cannot copy the iTunes folder from the old disk to the new disk using Windows Explorer?