Hi, I will need to change the url of a large number of existing web pages when they are migrated to a refreshed website. Therefore, for some people who have bookmarked this, they will get a error page. I can't do a 301 re-direct on all of these pages. So is there a better choice than making the 404 error page very user friendly so people can find their right page? Thanks Simon

Why can't you do a 301 re-direct on all the pages - is it down to the number of pages?  It may be worth the time as it will:
- automatically forward visitors who have bookmarked as well as those that come from search engines that still have the old URLs in the index; and
- help he search engines to update their indexes with the new URLS and pass some of the value of the old URLS to the new.

The sitemap is a good idea to avoid dead ends if you absolutely cannot redirect.