The purpose of this study is to see if it is safe and effective to give a new anti-HIV drug combination to HIV-infected patients who have never taken nonnucleoside reverse transcriptase inhibitors (NNRTIs) and who have failed to respond to protease inhibitors (PIs). The drug combination will contain didanosine (ddI) plus stavudine (d4T) plus nevirapine (NVP) plus MKC-442. Hydroxyurea (HU) may be added.