cannot download song

I need and MP3 version.

Mrgre,

The iTunes Store does not sell MP3s. if you need an MP3 either (1) download the AAC from the iTunes Store and convert its format, or (2) purchase an MP3 from Amazon Digital Music.

what is AAC??? I REALLY need MP3's RIGHT now to complete a project. Am willing to pay but don't see any option to purchase. The MP4s are protected. How do I get around this ??