Setup your web server to use custom ErrorFiles, from there you can setup the page to process the people directly to your homepage. My favorite was to write a errorpage in PHP that looked what URL people tried to goto, if it ended in the file extension (ie: .cfm) that I changed to .php it automaticly directed them to the right .php page, if it wasnt from a .cfm page on my webserver it sent them to my homepage.
I think it's a good idea to place the following meta tags on the webpage you use for errors. Most Linux systems will give a 302 code to search engines, which is a re-direct. These meta tags will make is clear that you're not up to something bad with your re-directs. Just my opinion.