Due to my work in web marketing and research for admin related sites etc.. i do encounter this question several times on blogs, forums and troubleshooting sites. I have also very recently received an e-mail from a blog reader asking me the very same question.
I have recently found this great post with some Tips on installing Exchange 2007 in to an Existing Exchange Organisation that could be helpful for anyone venturing into this change.
This post is written by Andy Grogan and he can be considered as quite an expert in this topic. You can view Andy’s blog on the following url http://telnetport25.wordpress.com