A question we get a lot these days concerns whether you can upgrade an existing Configuration Manager 2007 site running the 120 day evaluation version of the software to the retail version when it's available. In short, yes you can. We actually document this here. If you take a look at the note it states:
"It is supported to upgrade a site from evaluation version software. For example, you can run Configuration Manager 2007 Setup to upgrade an existing Configuration Manager 2007 site running 120 day evaluation version software."
In case you're looking for it, you can download the eval version here.
I hope this helps as you plan your roadmap to System Center Configuration Manager 2007!