You'll need to decrypt the DVD's data first before you can use it. I would suggest using DVD Decrypter, available at www.doom9.net

After decrypting the DVD Video Object (VOB) files using DVD Decrypter, you'll need a program to convert them to AVI so you can use the video in Windows Movie Maker. I suggest using DGMPGDec (also known as DVD2AVI), also available on doom9.

If you would like a really nice graphical guide, it looks as if animemusicvideos.org has one available:
http://www.animemusicvideos.org/guid...g_with_dvd.pdf

EDIT: And it looks as if the guide uses the same tools I mentioned above. This should make things a little easier.

Hope this helps.