Grrrrr... Sorry, my brain wasn't in gear. No you are absolutely correct. You use .xls format.
I just got to thinking about using office, and .doc came out.
On my computers I usually use Libre Office, and I have also used KOffice (a linux based office suite).
The decision tables are very simple. They don't use formulas or anything complex. Basically anything that can read and write a .xls format file with multiple sheets will work just fine.
Sorry about the confusion.
Paul Snow