When you autoGenerate a Select button with a Gridview, to find the RowIndex for that particular row, you can use the SelectedIndexChanged Event.
Inside that event, try something like this (with a label called 'Label1':
Dim row As GridViewRow = MyGridView.SelectedRow
Dim intRow as Integer=Row.RowIndex
GridViewRow gvr = new GridViewRow();
gvr = dgdManageUsers.SelectedIndex;
int introw = gvr.RowIndex;