Migrate to new server with near 0 downtime.

[1clue]

Are you using some sort of version control software for your php/css/html?

This sort of situation is one of the more compelling examples of why that sort of thing is needed IMO. Put your entire site/sites into source control, check it out at your new server, get a recent copy of the mysql database up and going, and then test it before the changeover.

In the end, the final transfer can be what everyone else has already said, but to test it out in advance removes quite a bit of doubt and lowers your blood pressure to boot.

[rs2k]

Version control is not a problem. FTP and a few commands will easily get the site running on a new server. I'm just looking for a way to minimize the confusion the DNS change causes. During the change the DNS likes to swap back and forth between IPs. This causes havoc on a website that uses sessions. The sessions are stored in the database so I think using telling the old server to use the new server for MySQL during the DNS change will work best.