Need help with String.Format arguments

I think I got it now.

I got hung up on having to use the format string parameter in String.Format
() to specify the order AND width of multiple fields (IE: {1,-10}{2,-25})
when it would be much easier to just format individual field and then
concatenate.



So I have a listbox with the field names that the user selected
in the order they specified....

For Example:
listbox items/order
"Date"
"Desc"
"Price"

        private string CreateInvoiceLine( string sDate, string sTime, string sPrice, string sServiceDesc,
                                            string sServiceLevel, string sDriver, string sComment)
        {
            string sConcatenatedInvoiceFields = "|";
            string sFieldName;

            for (int nIdx = 0; nIdx < this.listBoxInvoiceItems.Items.Count; nIdx++)
            {
                sFieldName = listBoxInvoiceItems.Items[nIdx].ToString();
                Debug.WriteLine(" - " + sFieldName);

                if (sFieldName == "Date")
                {
                    // All we are formatting is the width/alignment
                    // Field # is irrelevent ??
                    // Append the formatted field
                    // loop should put fields in proper order
                    sConcatenatedInvoiceFields += String.Format("{0,-15}|", sDate);
                }
                
                else if (sFieldName == "Time")
                {
                    sConcatenatedInvoiceFields += String.Format("{0,-12}|", sTime);
                }

                else if (sFieldName == "Price")
                {
                    sConcatenatedInvoiceFields += String.Format("{0,-10}|", sPrice);
                }

                else if (sFieldName == "Service Description")
                {
                    sConcatenatedInvoiceFields += String.Format("{0,-25}|", sServiceDesc);
                }

                else if (sFieldName == "Service Level")
                {
                    sConcatenatedInvoiceFields += String.Format("{0,-25}|", sServiceLevel);
                }

                else if (sFieldName == "Driver")
                {
                    sConcatenatedInvoiceFields += String.Format("{0,-10}|", sDriver);
                }

                else if (sFieldName == "Comment")
                {
                    sConcatenatedInvoiceFields += String.Format("{0,-25}|", sComment);
                }
            }
            sConcatenatedInvoiceFields += "\n";  // End the line

            Debug.WriteLine(sConcatenatedInvoiceFields);
            return sConcatenatedInvoiceFields;
        }


Sample runtime data: 
"|12-17-2007     |  75.00   |service description      |"
"|12-23-2007     |  50.00   |test test test           |\n"


I appreciate your assistance.