The primary objective of this study is to assess the safety and tolerability of tipranavir (TPV) oral formulation and soft gelatin capsules together with low-dose ritonavir in HIV-infected children and adolescents, to provide information concerning the pharmacokinetic characteristics of tipranavir and ritonavir in this age group, and to determine the relative bioavailability of the TPV liquid formulation and TPV capsule formulation in adolescents switching from liquid to capsule.