You are better off redirecting 404's to a page where you can provide alternative options for the customer, eg. links to sitemap etc.
To redirect 404 error to a static page, create a new 404 error static page, noting the page ID number.
Then edit /include/func/func.core.php
After...
Code:
@header("HTTP/1.0 404 Not Found");
Insert...
Code:
header('Location: http://www.yourstore.com/pages.php?pageid=123');
Or, to just redirect to the homepage, insert...
Code:
header('Location: http://www.yourstore.com');