So… when you have the Opsmgr 2007 console installed – on your laptop, for example – and you try to install the OpsMgr 2012 console, the installation performs an upgrade of the 2007 components (as expected, really). And this is all great and everything if you have upgraded your OpsMgr environment(s) to 2012.
But the OpsMgr 2012 console does not allow you to connect to an OpsMgr 2007 environment (and the reverse is also true). So what do you do if you want to connect to both 2007 and 2012 from the same machine?
Simple, install the OpsMgr 2012 console first (or allow it to upgrade the 2007 console), and then…. you just install the OpsMgr 2007 console again. Now they will happily co-exist, and you can even have them running (open) at the same time