Help needed to Rectify Google Webmaster errors - Basically 404 errors

Hi, My google webmaster is showing me errors URL Not found - 404 errors . I am having a shopping site and my site has about 4000 items and items tend to get finished off also so i normally Disable or Delete the items from the backend - AND i have observed that the google Webmaster shows me errors ( 404) for those items that are now not existant on the website. I need someone to help me with some script that I can install and get this situation rectified. One of the suggestions i have is that we can route the non-existant items URL to index page .... this is just one of the suggestion - you may have better solution . PLEASE let me know the solution and help me get it installed ( My shopping site is based on Magento) -i will not be able to give you access to FTP details of the site - SO you will guide me how to do it, However i will give you access to my google webmaster account so that you can also see what errors are there. Important: The solution that you provide me should be in compliance with google guidelines and my site whould not get penalized . Warm regards sanjeev