SpreadsheetGear does not make available the original values as found in in the CSV file (such as "00000000" in your case). You would only be able to access cell data after it has been parsed and processed by SpreadsheetGear (i.e., converting the above to a double value of 0). If you need the CSV's original values, then you'll need to open up file yourself and manually process and parse it.
It sounds like you ultimately want a DataTable, but if you still require to create a workbook file from your CSV data, once you've created a routine to manually open and parse each "cell" in your CSV file, you could enter each value into a spreadsheet as Text, so that it is preserved as it is found in the CSV file. You can go about this in two ways:
1) Set IRange.NumberFormat to "@", which will treat any future input into that IRange as Text. Example:
worksheet.Cells["A1"].NumberFormat = "@";
worksheet.Cells["A1"].Value = "00000000";
2) Prepend your inputted value with a single apostrophe, which indicates that you want the input to be treated as text. Example:
worksheet.Cells["A1"].Value = "'00000000";
If you still need a DataTable at this point, you could use the IRange.GetDataTable(...) method to accomplish this. Because the cell data is stored as Text, your DataTable values should also reflect these same values Example:
DataTable dt = worksheet.Cells["A1"].GetDataTable(GetDataFlags.None);
(There is a GetDataFlags.FormattedText option, but this isn't really relevant for your case since the cell data is stored as text anyway and so won't be formatted)