In part 1, patients will receive 1592U89 monotherapy for 12 weeks. Patients will be assigned initially to a low dose of 1592U89 (Dose A). Those patients who tolerate the drug for at least six weeks without a toxicity of grade 3 or above attributable to study drug will have their 1592U89 dose increased (Dose B). If none of those patients experience a life threatening event attributable to study drug, subsequent enrollees will be assigned initially to Dose B. In part 2, each participant will be assigned randomly (1:1:1:1) within their age and Part 1 regimen stratum to one of the four agents: Zidovudine (ZDV), Stavudine (d4T), Didanosine (ddI) or Lamivudine (3TC) in combination with 1592U89.