You have two other choices that do not use ActiveX.
1. If you write continuous data that exceeds the maximum number of rows in Excel, you can still read the data using an Excel macro. Using the ReadLine method, you can parse the data into cells and skip to the next worksheet when the row limit is reached or using any token that you want (ie. blank line).
2. If you have Excel 2000 or later, writing your data as an XML file will allow you to format the data into worksheets. This will increase the file size dramatically. To do this you have to write the required header and then maintain the proper heirarchy of Workbook, Worksheet, Table, Row, Cell and Data. Save a simple data file as XML to see the file format.