Word.Basic will always reference the latest version of MS Word. It also appears that the two interfaces are binary compatible because they both have the same Class IDs.
(I only have Word 2000 on my system, but Word.Basic, Word.Basic.8 and Word.Basic.9 have the same CLSIDs, plus microsoft knows that it is important to have binary compatibility)

Anything you implement using Word 97 should work fine with Word 2000.