I have a 4 year old small ecom site, my field is relatively small and is a boutique cottage industry. I have however gained some good search results in the relevant words.
I am about to change over to an extensively modified and customised zen cart system on a different server. The reason is to offer customers a much better shopping experience and to use the powerful script to streamline my administrative process.
My worry is how to change the site over. I can use the same text in the product descriptions and semi SE friendly URL generation but the end result will look completely different to search engines.
1. Should I attempt to run the existing site along side the new one and link over to the new site?
2.The new site features extensive Java script navigation. I read elsewhere
JS rollover buttons hiding the internal link structure
I really like the JS rollover menu for ease on navigation. Is this a major SEO problem and can JS Menus it be used effectively.
Now for #1 -- if your change the url in any way that is a new page in the search engine's view. If you continue to run the old url, but the dynamic url has the same content, the new url may not ever be indexed. I'd suggest a 301 redirect from important static urls to the new dynamic pages. It may take the search engines a while, but eventually all should be sorted out.
for the js navigation their might be a solution that would both please you and the search engines. I am assuming that by js navigation you are talking about drop downs / drop boxes, and if so try googling for 'suckerfish navigation'.
Regarding the new site / new pages I'm with tedster on this one, if you want to use the same text on the pages it would be wise to implement a 301 permanent redirect or 301 redirectmatch (if the url change follows a recognisable pattern).
If you have the good position and are afraid to lose them, you could always have both sites running and change the content/copy of the new one.