On my machine I have two versions of Excel (Excel X for Mac and 2011). I installed the latest version so that I could access some of the new features in Word that are not in the old version. However, I wanted the majority of my Excel files to open with the old version. However, when I use the Get Info command on an individual file which allows me to choose the opening application it seems to lose the settings upon closure. Even with the old version selected if all apps are closed and that file is opened it will open with the new version. If the old version is running, then no problem the Excel file opens in that version - but it always defaults to the new version if both apps are closed. This means that before opening a file you have to launch the app version you need. Frustrating. Is there a work around for this? Needless to say the Change All option of having all files open with the old version is equally inoperative.
MacBook Pro 2.4 GHz, 250GB drive. 4GB RAM, Mac OS X (10.6.6), Using external Cinema Display
As a workaround, might be able to save some keystrokes by keeping an icon for the earlier version of Excel in the Dock. Then when you want to open an Excel file there, just drag the Excel file's icon onto that Dock icon.
I don't have two versions of Office, so I haven't been able to test this to be sure that such a Dock icon will "remember" its version when both apps are present in the system but not currently running.