A Randomised Trial to Evaluate the Antiviral Efficacy and Safety of Treatment With 500 mg Tipranavir (TPV) Plus 100 mg or 200 mg Ritonavir (RTV) p.o. BID in Comparison to 400 mg Lopinavir (LPV) Plus 100 mg RTV p.o. BID in Combination With Standard Background Regimen in ARV Therapy naïve Patients.