Why would you need to convert to avi. Windows Media Player reads Mpeg1 and Mpeg2(if you have the mpeg2 codec installed on your comp, please read the guides) which are of significantly better quality res. wise. Just use DVD Decrypter and rip the DVD then use DVD2SVCD and convert to either Mpeg 1 or 2 depending on whether you want low or high quality respectively.(again read the guides for this)
Hope this helps.