The main purpose of the study is to measure changes in the blood lipids and to compare these between patients who start with either an SQV / RTV-containing regimen or an ATV / RTV-containing regimen. In addition, the changes in fat distribution, sugar metabolism and insulin sensitivity will be compared between these groups. Possible changes in bone density and renal function will also be examined. Furthermore, the virologic effectiveness and overall safety of the two treatments will be evaluated and compared.