Wal-Mart on Thursday began a public test of its new 88-cent-per-song online music service, which undercuts the 99-cent standard set by the iTunes Music Store. The world’s largest retailer is offering “hundreds of thousands” of songs in Windows Media format. The songs can be transferred to compatible portable devices, burned to a CD or played on Windows-compatible PCs. Wal-Mart plans to officially launch the service in 2004.