I know there are plenty of folks out there who have had to SUFFER to try and work through an installation/integration of MOSS2007 with SSRS2008. I recently ran across a blog posting with a FANTASTIC description of how the process works, in an environment that has 3 machines. Do yourself a favor and read this blog post if you need to do this setup. It will answer a lot of questions.

http://mosshowto.blogspot.com/2009/03/reporting-services-sharepoint-multiple.html