To determine the potential effects of 28 days of nevirapine treatment on the steady-state pharmacokinetics of nelfinavir and of stavudine (d4T), and to further evaluate the pharmacokinetics of nevirapine in combination with nelfinavir, and d4T compared to the historical controls treated with nevirapine but without nelfinavir or d4T. To determine the efficacy of long-term combination therapy of nevirapine, nelfinavir and d4T on viral load in patients who are non-nucleoside reverse transcriptase inhibitor (NNRTI) and protease inhibitor naive, and have <= 6 months prior d4T exposure at the time of screening.