You can dual install a copy of AE 6.5 and 7. I have done it for a while to compare our plug-ins on Mac and Windows.
BTW: We are working on updating all plug-ins to be compatible with AE 7. Check our website for info. early next week. Most of the issues are on Mac becuase of changes to AE 7 to support the new framework. Adobe made the Mac version a Cocoa-based application so that they can eventually move to a universal binary. This is a major change for some plug-ins because certain features that plug-ins depend upon like dialogs and palettes require a switch to Apple’s developer tools.
Sean Safreed
Red Giant Software
http://www.redgiantsoftware.com