The objective of this study is to establish the tipranavir-ritonavir steady-state dose-exposure relationships when administered on a b.i.d. dosing regimen; to determine the effects of tipranavir (TPV) and ritonavir (RTV) on cytochrome P-450 (CYP3A4) activity; to establish the dependency of the TPV M1 metabolite on RTV co-administration. Additionally, the short-term safety and tolerance of this drug combination will be evaluated.