Adobe Creative Suite 4 will support 64bit OSes running Windows, whereas for Mac, it will still be 32bit only. When Adobe Creative Suite 5 comes, it will support both 64bit OSes in Windows and Mac.

What’s Adobe doing with Photoshop? In the interest of giving customers guidance as early as possible, we have some news to share on this point: in addition to offering 32-bit-native versions for Mac OS X and 32-bit Windows, just as we do today, we plan to ship the next version of Photoshop as 64-bit-native for Windows 64-bit OSes only.

The development is frankly bittersweet for us: On the one hand we’re delighted to be breaking new ground with Photoshop, and when processing very large files on a suitably equipped machine, Photoshop x64 realizes some big performance gains. (For example, opening a 3.75 gigapixel image on a 4-core machine with 32GB RAM is about 10x faster.) On the other hand, we work very hard at maintaining parity across platforms, and it’s a drag that the Mac x64 revision will take longer to deliver. We will get there, but not in CS4. (Our goal is to ship a 64-bit Mac version with Photoshop CS5, but well be better able to assess that goal as we get farther along in the development process.)

Source: John Nack on Adobe: Photoshop, Lightroom, and Adobe’s 64-bit roadmap