This study was designed to evaluate and compare safety, tolerability of subjects who successfully suppress HIV-1 on their first PI regimen to those who switch to fosamprenavir. This is a 48-week study, where subjects who were assigned to be in their original PI-group have the option of switching to fosamprenavir on week 24. Prior to being assigned their treatment group, subjects had to be suppressed for at least three months. All subjects also take a background regimen of two nucleoside/nucleotide reverse transcriptase inhibitors.

Inclusion Criteria:

• Be on your first protease inhibitor (PI) containing regimen, and the regimen must consist of a PI +/- ritonavir and 2 Nucleoside/Nucleotide Reverse Transcriptase Inhibitors (N[t]RTIs).
• Have a plasma HIV-1 RNA level (viral load) at screening of less than 400 copies/mL, for at least 3 months prior to Screening and at Screening while on your current regimen of a PI +/- ritonavir + 2 N(t)RTIs.
• Females must not be pregnant or breastfeeding or plan to become pregnant during the study.
• Females of child-bearing potential must agree to use one of the approved methods of birth control.

Exclusion Criteria:

• Not able to follow the medication schedules and attend the study visits for the entire length of the study.
• Have any other illnesses, laboratory test results, medication use, allergies, or medical conditions that would make it unsafe for the subject to participate in this study.
• Currently be enrolled in any other research studies that could affect the subject''''s HIV-1 RNA levels.