Change alignment of Cell in Excel and separate number digits by separator (use Excel in c#)

Hi
I Use DCOM Excel component for export my data to Excel . but I face to 2 problems:
1- How can I set align of a text in a cell ? set it to right , left or center. For example worksheet.cell[1,2].align = “right”;
2- Suppose Contains of a cell is a number . I wants to separate it’s digits by separator (3 digits by 3 digits) for example : 34567898 to 34,567,898
Thanks very much