To assess the safety and efficacy of itraconazole versus placebo for prevention of histoplasmosis in HIV-infected patients with CD4 counts < 150 cells/mm3 who reside where histoplasmosis is endemic. To assess the safety and efficacy of itraconazole for preventing other debilitating fungal infections, such as cryptococcosis, aspergillosis, recalcitrant oropharyngeal or vaginal candidiasis, and recurrent esophageal candidiasis.