I am currently designing a new website in Xara Web Designer Premium for a local community centre. The old website is a Joomla site. This means all the URLs will change. (Joomla uses php whereas Xara uses htm files). The URLs will also, generally speaking become shorter. The new website is at least going on the same main domain. These changes mean that any links currently displaying in a Google search will stop working unless I can add 301 re-directs.
Does anybody know if there is way to do this in a batch method rather than trying to pick up each page individually? Ideally, where there are equivalent pages I would like the re-direct to go to its new equivalent but if this is not possible I'll take the best I can get.

Would a 404 "page not found" work better (Assuming it could be set-up to react to any inputted URL from the old website), provided I included a new nav bar on the 404 page?

Obviously I'm concerned about losing what little google search engine ranking we may already have, but more particularly about potential users clicking on a redundant google link and then being lost.

Thanks for your time.