What's the Worst that Could Happen?

::: calling experienced developers & marketeers :::

[subway]

I have read lots about spiders indexing database driven sites, etc, etc, and know myself from experience that most big engines handle them, very nicely.... however I have one particular client with a very well ranking, busy site of about 150 HTML pages that needs to go dynamic - all of it as I can no longer stand to attention and act immediately whenever he needs a picture changed.

So my question is...

Bearing in mind he won't change his domain name (it's all over the corporate stationary) and in order to change the site I need to move servers (same company but different IP) what is the worst that I can expect, if I keep all the links the same on everypage, etc.

Will the site continue to get visited by the spiders, will it get kicked out, drop in the SERPS, gain in the SERPS, etc...

The only major differences are going to be the urls or page names.

Thanks in advance.

[deft_spyder]

seems like an instance where you'd want to use the permanent redirect function.