I have a document of 200 pages in MSWord 2003, of which 20 consecutive pages contain tables. I want to fix these tables so that they do not shift from their original position; moreover these tables are susceptible to frequent changes(insertion of new rows and deletion of existing rows). What is the best method to ensure the table formatting and their position?

The only thing I would suggest is a CTRL-ENTER before each table to insure it is situated at the top of its page.

If you're inserting/deleting rows, there's nothing you can do about how long each table is, it is what it is. But making sure each table starts at the top of a page will at least keep changes in one table from affecting the others that follow.