>Im moving development from 5.0 to 6.0, with a few users piloting my 6.0 versions of a long running app. I need to distribute 5.0 apps to other users probably for about 5 more months.
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>Whats the best way to install 6.0 on my machine so I still can develop in 5.0 as well?

All you have to do is make sure you install it in its own folder. It will happily co-exist with 5. When you get 7, you can have all 3 versions installed and working serparately. Just install in their own folders.