Hi

I am in the process of rebuilding a site from static pages to a CMS which will be using mod_rewrite to generate new page URLs. In this process our marketing people and myself have decided to tidy up the descriptions, keywords and titles.

Eg: a page which who's URL is currently "website-name/about_us.html" and has a title of "website-name - something not quite page specific" will change to "website-name/about-us/" and title: "about us - website-name" and may have a few keywords and the description changed.

Our goal with updating the meta data is to improve our page rankings and try to keep in line with some best practices for SEO. Though our current page rankings are quite good in many aspects, there is room for improvement.

All of the pages will also have content changes (like rearranging heading tags, new menu on all pages, new content in footer, extra pieces of dynamic content relating to other pages).

In this new site process I plan to use 301 redirects for all the old URLs pointing to the new URLs.

My question is what can I expect to happen to the page rankings in Google, in the sort term and long term?

Will this be like kicking off a new site which will have to build up trust over time or will the original page rankings have affect?