|Transferring FSMO roles is the same whether you do it from 2003 to 2003, or from 2003 to 2008. See this article below:|
I assume that you want to replace the exchange 2007 server with the exchange 2010 server. I first want to point out that you can't do an in-place upgrade of 2007 to 2010, you have to have two separate servers for the process. There are so many variables for upgrading Exchange, so I'm not going to give you specific advice. Start with the link below. If it's too overwhelming, hire a consultant. You don't want to screw up your whole company's email system just to save a few bucks.
BL Technical Services
IT Support Maryland