Music is unlocked when you complete ALL the stages in a particular section of the game.
Unlock Croft Manor Music:
Complete Croft Manor.
Unlock ALL Egypt Music:
Complete Temple of Khamoon, Obelisk of Khamoon, Sanctuary of the Scion.
Unlock ALL Greece Music:
Complete St. Francis' Folly, Coliseum, Palace Midas, Tomb of Tihocan.
Unlock ALL Peru Music:
Complete The Lost Valley, Mountain Caves, City of Vilcabamba, Tomb of Qualopec.
Unlock ALL Lost Island Music:
Complete Natla's Mines, The Great Pyramid, Final Conflict.
Added by: Sanzano Jan 9th 2008, ID#12015