What is the best way to move a well-ranked site?

Changing design and IP of site.

[inbound]

I'm doing work on behalf of another company who insist on moving the hosting of a site (hence a new IP) for a redesign that they are undertaking.

My fears are that doing both will make Yahoo and other engines suspect something is amiss, do you have any advice on how to do this without threatening the #1 position that the site has for their core business terms?

The reason the site is changing is it needs to convert more sales otherwise it wouldn't be being re-designed.

[blaketar]

The IP move should be minimal, may take a couple of days but do not get frantic!

Site design is another issue completely. My advice would be to migrate the design (new links, pages, etc.) over time. Start by adding a few main topic links within the home pages or well-indexed pages of the current site. As these new pages and links become indexed start 301'ing the old pages to the new.

I would really evaluate taking 6 months to 1 year to make the complete transition if the site is the main core of business and ranking is a must!