Complete Redesign

[cslhypnotech]

Hi,
We're currently revamping all of our websites. I've been trying to find the best way to do this without losing our rankings(currently ~1-10 for our top keywords). From what I've read, doing a complete site redesign(layout, content, filenames, extensions, etc.), is going to greatly affect our SERP placement. What is the best way to go about this? 301s? Sitemaps on 404s?
Also, what would be a good way to work around this in the future? Does the idea of using folders as links(ie, domain.com/contact vs domain.com/contact.php) work?

[KeithO]

yeah, you're going to experience major changes having everything redone. Do 301 redirects for the existing content pages and you might be ok.