Not sure if these are allowed on here (Chemo made them!) but attached are two php files that generate xml files on the fly. Create a Google Sitemaps account and Google will crawl the page regularly without the need for Cron jobs or any file tweaks. This also works with Chemo's SEO contribution.
No work at all done by myself; all credit to Chemo.
Support thread: http://forums.oscommerce.com/index.php?showtopic=282968
Again all thanks to Chemo.