..from:
http://labs.adobe.com/technologies/photoshopcs3/


For the first time ever, Adobe is delivering a widely available Photoshop CS3 beta to enable customers to more easily transition to the latest hardware platforms, particularly Apple's new Intel based systems. The beta is available as a Universal Binary for the Macintosh platform as well for Microsoft Windows XP and Windows Vista computers, with the final shipping release of Adobe Photoshop CS3 planned for spring 2007.

[...]

The Photoshop CS3 beta is available in English only but to Photoshop CS2 users worldwide. It is available to licensed users of either the Photoshop CS2 (full, upgrade, and education), Adobe Creative Suite 2 Standard or Premium (full, upgrade, and education), Adobe Production Studio Standard and Premium (full, upgrade, and education), Adobe Video Bundle (full, upgrade, and education) or Adobe Web Bundle (full, upgrade, and education). You will need to provide your Photoshop CS2, Creative Suite, Production Studio or Bundle serial number in order to get a Photoshop CS3 beta serial number, enabling you to activate the Photoshop beta and use it beyond the two-day grace period.

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....and from a "Welcome Letter" from the Photoshop Group Product Manager:

December 15, 2006
Dear Adobe Photoshop Customer,
Welcome to the Adobe Labs site, a place where you might not have expected to go to find the latest
version of Adobe Photoshop!
We’re taking the unprecedented step of making a beta version of Photoshop CS3 available today,
primarily because we know that our Macintosh customers will appreciate the opportunity to start
running Photoshop natively on the latest Intel based Macintosh systems, months before the final
shipping version of the product is ready. Of course, we know that it wouldn’t be fair to our Windows
customers to exclude them from this advance preview, so we’re releasing the beta for you as well.
Our final Photoshop CS3 feature set is already largely determined, based on input from thousands of
customers like you. Note that the beta version that we are releasing today might not look exactly like
the final shipping version. There are still a few planned features not yet implemented, and of course
some polishing and bug fixing we still need to work on. You’ll however find a wealth of new features
to explore in the beta. I encourage you to take a look at our new feature list for some ideas of what to
expect.
Ultimately, though, this beta release is less about showing off our new features than it is about getting
native software to our customers as soon as we can. I hope you like what you see, and that you decide
the upgrade is a great value when we release it later in 2007!
And as always, my team and I thrive on your feedback, and it will certainly influence our plans for
Photoshop CS4 and beyond.
Regards,
  Maria Yap
  Group Product Manager 

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Adobe Labs Beta download site:
http://labs.adobe.com/