Changing the URL for 1000's of pages

Is there a "safe" way to do this?

[ALbino]

Right now my site is set up like this:

[widgets.com...]

I did that originally so that I could get indexed by Google without being dynamic. I've since come to realize that some other engines (Altavista for example) won't spider the site past any root URLs I believe because the .php extension stops them. For example it will spider new.php or category.php but not new.php/date/ or category.php/item/. I gather from posting on the other forums that if I change it to /new/date/ or /category/item/ that it will be spiderable. However, we all know Google is the most important engine and I have great SERPs on Google for many keywords and combos and I would never touch anything with a ten foot pole that could disrupt that. I was just wondering if there's a "safe" method of changing the entire structure of your site around and still being able to maintain rankings and PR. It seems unlikely, but I thought I would at least ask. Thanks.

[Jeff_H]

To do this I would:
(1) make the changes to mod_rewrite (or whatever you are using) so that your pages are at browse/category/item/

(2) make a folder called category.php and put a permanent redirect it the .htaccess

/browse/category.php/.htaccess =
Redirect permanent /browse/category.php/ /browse/category/

check the syntax on the about though, but that's the generaly idea, so that

/browse/category.php/item4934 redirects to /browse/category/item4934

Google should pick up the redirects