The Adobe AIR 1.0 release will install side-by-side with any beta releases already on the target machine. Applications which are bound to the beta releases will continue to run on those releases until the beta releases themselves expire. That's June 1, 2008 for Beta 2 and November 1, 2008 for Beta 3.
Users with either (or both) beta release installed will be automatically updated to 1.0 the first time they encounter an application bound to 1.0. This is true regardless of whether it's a new installation or an update. I described this in more detail in this earlier post on the auto-update mechanism.
...
More details at the source...