you can use the automation (loading excel into memory as an object and using it programmatically) to convert the file to csv..
..or you can use the Microsoft Jet database driver in excel mode (
ConnectionStrings.com - Forgot that connection string? You will find it right here!) to access it like a db, read the file into a datatable, and then write it to disk as delimited text
See my recent edit to the other post about this topic being in the wronf section