Moving a website, help needed

I am re-developing a website that launched 8 yeas ago. When the site launched it was developed in TCL and had an Oracle back end. The site's previous developer is still hosting the site on his server.

Long story short, we are re-developing the site on a new server at a different location. We'd like to re-launch on the old server (to help maintain Google search rankings), but we are developing in .Net and SQL. The old server is Linux. We want to maintain our ranking on Google since we are "Top Ten" on more than 20 great keyword phrases.

If we use a DNS forward from the old IP to the new one, are we going to loose rankings on Google? Obviously yes. But would it be beneficial to help the old developer buy a SQL server so the DNS forward is to a server 2 feet away as opposed to across the country? Does Google treat these equally?

Any insight?

Moving the IP address of the hosting server will not make any difference at all to rankings, unless you go and host in some black-listed area, but I can't see that happening. The biggest thing that you need to be sure of is that there's no down-time on the move, so be sure that the new site is up and running before you change the DNS records for the domain name. That way no one will be left out in the cold.

Got it. But We can't keep the same IP address, can we? I was told the current IP is one of 16 "logical IP" attached to one physical one on the server.

It sounded like when we re-launch, I will have a new IP address. Is there a way to take that old one and use it on the new IP? I was given the new IP by the hosting company we're renting a SQL Server from.

Given that, how does changing the IP effect Google? Greatly?