When will iTunes replace Wal-Mart as No. 1 music retailer?

Apple's iTunes will likely whip past Wal-Mart Stores to become the largest U.S. music retailer sometime this year.

The NPD Group issued a report Tuesday that said Apple had outpaced Best Buy and Target to become the No. 2 U.S. music retailer. Unless the downward trend in CD sales suddenly reverses, Apple will be No. 1, said Russ Crupnick, the NPD Group's president of Music.