how does the data actually come? is it a real csv file, and not an excel doc?
I've imported millions of rows via bulk insert or SSIS with delimited files, which would be my preference;
excel 2007 doesn't handle lots of rows too nicely, i believe , and can manipulate the data to what it THINKS the data should be, instead of what it really is.
I've also automated excel in .NET ,and it's frustratingly slow when it's processing a Range line by line.
Lowell