The main objective of the study is to assess changes in fat distribution over 48 weeks of treatment in patients who currently successfully use zidovudine (AZT) and lamivudine (3TC) as part of their regimen and who will either continue these antiretrovirals or who will switch these antiretrovirals to tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC). Each of these medications is commonly used for the treatment of HIV-1 infection.