By big album art I am assuming you mean on your lock screen when music is playing and as your background in Zune, right?
Basically, if you are in a Zune supported area (US, Canada) for example then Zune should technically grab the image automatically and add it to the mp3. But if it doesnt work you can always add the cover art yourself by using a program like Mp3Tagger or Winamps MP3Tag (freeware) http://www.mp3tag.de/en/ or http://ostermiller.org/mp3tagger/
Basically, use the mp3tag program of your choice and use it to add album/cover art to you songs. It works for the most part but some tracks just refuse to show album art, and that is a Zune issue.





