Well, the answer now depends on what version of Word you're using, and what
version the other user is using. If you're both on Word 2003, then it is
possible: Using the Protect Document task pane, you set the document to "No
changes (Read only)" and then set exceptions for the last three columns of
the table (and any other parts of the document where you want to allow
editing).

If you don't have Word 2003, then forget about it. If the other user doesn't
have Word 2003, the whole document will be locked, so again you can forget
about it.