Principal Component Analysis and Clustering

Hello, I'm studying a problem of clustering. Given a data set of n features (columns), I use PCA to get only 2 first principal components of these n features. Then I use a method of clustering to identify 3 classes of the scores of PCA. Graphically, the function 'gname' can show me the row number of each score when I click on it. Is there a command line to show the row numbers of all scores clustered in one classe ? Thanks for your help Regards, Winn