Safety and Effectiveness of Adding Adefovir Dipivoxil and Nelfinavir to the Anti-HIV Therapy of HIV-Infected Children

Inclusion Criteria Your child may be eligible for this study if he/she: * Is 3 months to 16 years old. * Is HIV-positive. * Has never taken protease inhibitors or has previously taken ritonavir (RTV), saquinavir (SQV), or indinavir (IDV) and is willing to stop the medication at study entry. * Is taking an anti-HIV drug combination that will not change during at least the 2 weeks prior to study entry. * Agrees to use effective barrier methods of birth control, such as condoms, during the study. * Has consent of parent or guardian. Exclusion Criteria Your child will not be eligible for this study if he/she: * Has ever taken NFV. * Has a history of opportunistic (AIDS-related) infection. * Has any disease or illness that would prevent him/her from completing the study, including cancer. * Has taken certain medications, including protease inhibitors at study entry. * Is receiving an HIV vaccine at study entry. * Is pregnant.