To determine the steady-state pharmacokinetics of 141W94 in combination with saquinavir, indinavir and nelfinavir after multiple oral dosing. To determine the steady-state pharmacokinetics of saquinavir, indinavir, and nelfinavir in combination with 141W94 after multiple oral dosing. To assess the safety and tolerability of multiple doses of 141W94 when combined with saquinavir, indinavir and nelfinavir.