How can I add an album to itunes so it stays as an album?

I have an album. On the album are 12 tracks.

The album has already been ripped to my hard drive and lives in a single folder,.

When I 'add folder' to itunes, it gives me a convert from WMA message (fine) and starts the transfer. My album arrives in itunes, the first song arrives in the album, the correct album artwork appears, song 2 arrives all looks good until song 7 which has a 'featuring xxx' additional singer. Instead of adding song 7 to the same album, a new album is created with JUST song 7. Then song 8 arrives in the original album, and then song 11, who was a different vocalist becomes a third 'album' on its own.

I obviously want the album to be one - containing all songs in the order I bought them! How can I stop itunes doing really annoying things and making decisions I dont want it to make?

I couldn't resisit trying a "Various Artists" album - you've already guessed it. 12 different 'albums' in itunes, all with the same title, all with the same artwork, all containing only one track!

Can anyone help me make sense of this?

Trevor