Patients are allocated as follows: a) zidovudine-naive patients switch Combivir for d4t and b) zidovudine-experienced or -intolerant patients switch abacavir for d4t. Providers may choose between Combivir or abacavir as a switch for d4t when screening lactate levels are 2.2 mmol/L or more. Additionally, providers may choose to switch a maximum of 2 drugs, one of which must be d4t, in the regimen. Each patient receives 48 weeks of therapy. Visits are made at Weeks 2, 4, 8, 12, 16, 20, 24, 32, 40, and 48. Tests, including biopsies, are performed to measure changes in body fat distribution and changes in lactate levels. Virologic and immunologic outcomes, changes in physical signs of lipodystrophy, changes in self-reports of health-related quality-of-life survey and the Body Image Questionnaire, changes in lipid profile and other markers of metabolism, and safety parameters are evaluated also.