[...]
<sarcasm Good ol' M$...</sarcasm

Seriously, according to the KB article posted above:

"Microsoft Excel can open and view a Works Spreadsheet document in its
native (.xlr) format. A Works Spreadsheet document can be viewed with
any program that can open or view a Microsoft Excel worksheet.
Additionally, Spreadsheet can also open Backup files (.bks) and Text
files (.txt)."

Hi LeAnne
but this is probably not the default format to save a Works file. If the
user has the option to create such file in Works he could create a *.xls
file anyway :-)

Frank