The purpose of this study is to evaluate the safety and effectiveness of 2 drugs (AmBisome versus voriconazole) in treating fungal infections. Immunocompromised patients, especially those with persistent fever and neutropenia, are at a high risk of developing deeply invasive, life-threatening fungal infections with Candida, Aspergillus, and other opportunistic fungal pathogens. The risk of fungal infection increases in direct proportion with severity of neutropenia and duration of fever. Antifungal therapy, therefore, is an important step in the amelioration of fungal disease.